UNIVERSITY of OSLO SSS DEPARTMENT of PHYSICS Iu Ji 11 I

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UNIVERSITY OF OSLO SSS

DEPARTMENT OF PHYSICS REPORT SERIES

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Ih AM LI jjj Ui U-JJJ jjJIlfclfcifcifc.N We regret that some of the pages in the microfiche copy of this report may not be up to the proper legibility standards, even though'the best possible copy was used for preparing the master fiche SECTION for NUCLEAR PHYSICS AND ENERGY PHYSICS Annual Report

January 1 — December 31 1992 UiO/PHYS/93-08 Received 19 - 04 - 1993 ISSN-0332-5571 O f* - - ^ "i - ? Contents

1 Introduction 5

2 Personel 6 2.1 Research Staff 6 2.2 Technical Staff 6 2.3 Visiting Scientists 7 2.4 Students 7

3 The Cyclotron 8 3.1 Operation and Maintenance 8

4 Data Acquisition and Analysis 9 4.1 Introduction 9 4.2 Configuration 10 4.3 Acquisition and Data Analysis Software 12 4.4 The CAMAC Pile-Up Rejection Module (PUR) 13

5 Nuclear Instrumentation 14 5.1 The CACTUS Project 14 5.2 The SIRI Strip Detector Project 15 5.3 The CHICSI Multifragment Detector 18

6 Experimental Nuclear Physics 21 6.1 Introduction 21 6.2 Nuclear Properties at Moderate Temperature 23 6.2.1 Extraction of Multiplicity Distributions 23

1 6.2.2 Spin Population in the 1MDy(3He,a)161Dy Reaction . 25 6.2.3 Nuclear Temperature in 3He Reactions 27 6.2.4 Level Densities in lMDy 28 6.2.5 Excitation Regions in 161Dy Feeding the Isotopes 161_IDy 30 6.2.6 Transferred Angular Momentum in the (3He,a) Reaction 31 6.2.7 Gamma-Ray Branching and the K Quantum Number in Even-Even Rare-Earth Nuclei 33 6.2.8 The K Quantum Number and the Decay of Neutron Resonances 34 6.2.9 Activities at NBI: Selective Studies of Hot Rotating Nuclei by Means of the Giant Dipole Resonance ... 37 6.2.10 Pre-Fission 7-Decay in Superheavy Nuclei 44 6.3 Rotational and High-Spin Nuclear Physics 48 6.3.1 Interpretation of Bands in 163Er within the Tilted Ro- tation Scheme 48 6.3.2 Delayed Crossing in the Unfavoured Signature Partner 163 of the h9/2[541]l/2- Band in Tm 50 6.3.3 Spectroscopy in the Odd-Odd Nucleus 162Tm 51 6.3.4 Angular Correlations in NORDBALL 52 6.3.5 Looking for M2 Admixtures in Sideband De-Excitations 53 6.3.6 High-Spin Study of 16SLu 53 6.3.7 High Spin States in 166Hf 55 6.3.8 Interpretation of the Rotational Band Structure in m,i72W The importance of Small Deformation Changes 56 6.3.9 Bandcrossings and the 71*13/3 Band in mRe 56 6.3.10 Octupole Deformed States in the Radium Region ... 57 6.3.11 Helium-Induced One-Neutron Transfer to Levels in 1MDy 58 6.4 High and Intermediate Energy Nuclear Physics 61 6.4.1 Isotopic Effects in Light Fragment Emission 61 6.4.2 Measurements of K+-Mesons at SIS 61 6.4.3 Strangeness Production in Ultrarelativistic Nucleus- Nucleus and Proton-Nucleus Collisions 62

2 7 Theoretical Nuclear Physics 66 7.1 The Nuclear Many-Body Problem and Nuclear Structure . . 67 7.1.1 Studies of the Effective Interaction for Finite Nuclei . 67 7.1.2 The Structure of Neutron Deficient Sn Isotopes .... 68 7.1.3 Isobar Contributions to the Imaginary Part of the Optical-Model Potential for Finite Nuclei 71 7.1.4 New Equations of State for Neutron Stars 74 7.1.5 Model-Space Brueckner-Hartree-Fock Calculations for Nuclear Matter 76 7.1.6 Nuclear Renormalization of the Isoscalar Axial Cou- pling Constants 77 7.2 Nuclear Reactions 80 7.2.1 Momentum-Depeadent Mean Field Effects on the Nu- clear Equation of State and on Phase Transition Signals 80 7.3 The Foundation of Quantum Physics 81 7.3.1 Quantum Theory and Questions of Reality and Com- pleteness 81 7.3.2 SQUIDs as Macroscopic Quantum Objects 85 7.3.3 The Conception of Ether and Phenomena of Light - from Descartes to Einstein 86

8 Other Fields of Research 37 8.1 Radiation Physics 87 8.1.1 Instrumentation for Simultaneous 220Rn and 232Rn Mea- surements 87 8.1.2 221Rn and 226Ra in Tap Water from Drilled Wells ... 88 8.1.3 Influence of Meteorological Factors on the Radon Con- centration in Norwegian Dwellings 90 8.2 General Instrumentation 91 8.2.1 The Design of a Pure Pitch Automate for Keyboard Instruments 91 8.3 Energy Physics 92 8.3.1 Solar Hydrogen - Hydrogen Produced from Renewable Resources 92 8.3.2 PV-Driven Electrolysis 93 8.3.3 A Study of Heat-Exchange Properties of a New Semi- Open Solar Collector Concept 96

3 8.3.4 Photolysis- Hydrogen Produced Directly by Solar Ra- diation 99 8.3.5 The Possibility for Combined Quantum/Thermal Con- verters 100 8.3.6 The Importance of Insolation Autocorrelation in Solar Heat System Calculations 101

8.4 Neural Network 103

9 Seminars 105

10 Committees, Conferences and Visits 106 10.1 Committees and Various Activities 106 10.2 Conferences 108

11 Theses, Publications and Talks 110 11.1 Theses 110 11.2 Scientific Publications 110 11.2.1 Nuclear Physics and Instrumentation 110 11.2.2 Radiation Physics 112 11.2.3 Energy Physics 112 11.3 Scientific and Technical Reports 112 11.3.1 Nuclear Physics and Instrumentation 112 11.3.2 Energy Physics 115 11.3.3 Educational Physics 115 11.4 Scientific Talks 115 11.4.1 Nuclear Physics and Instrumentation 115 11.4.2 Energy Physics 120 11.4.3 Radiation 121 11.4.4 Educational Physics 121 11.5 Popular Science 121 11.6 Science Policy 124

4 Chapter 1

Introduction

This annual report summarizes the research and development activities of the Section for Nuclear Physics and Energy Physics at The University of Oslo in 1992. It includes experimental and theoretical nuclear physics, as well as other fields of physics in which members of the section have participated. The report describes completed projects and work currently in progress. The experimental activities in nuclear physics are mainly centered around the Cyclotron Laboratory with the SCANDITRONIX MC-35 Cyclotron. Using the CACTUS riultidetector system, several experiments have been completed. Some results have been published while more data remains to be analyzed. The collaboration with foreign laboratories has continued in 1992. For many years we have participated in the Nordic collaboration, NORDBALL, at the Niels Bohr Tandem Accelerator Laboratory. Members of the section also participate in experiments at GSI, Darmstadt and GWC, Uppsala. At the end of 1992 13 students (for the degr*'« Cand. Scient.) and five post-graduate students (for the degree Dr. Scient.) were associated with the section. The cyclotron has continued to work satisfactorily due to the untiring effort of E. A. Olsen. The excellent job done by him, J. Wikne and J. Taylor in keeping the accelerator and data system in operation is highly appreciated by all of us. The basic costs of running the cyclotron laboratory is covered by the Uni- versity. The experimental activities, however, would not have been possible without the continued support from the Norwegian Research Council for Science and Humanities (NAVF). Finally, the efforts of Torgeir Engeland and Magne Guttormsen who have served as editors of this report, are appreciated by the other members of the Section. Blindern, March 1993 Svein Messelt Leader of the Section for Nuclear Physics and Energy Physics

5 Chapter 1

Personel

2.1 Research Staff

Sven L. Andersen Senior scientist Harald Andås Research ass. (NAVF) Trond Bergene Research ass. (NAVF) Bård Bjerke Research ass. Torgeir Engeland Professor Ivar Espe Senior scientist Kristoffer Gjøtterud Assoc. prof. Magne Guttormsen Assoc. prof. Ole H. Herbjørnsen Assoc. prof. Morten Hjorth-Jensen Research ass. Anne Holt Research ass. Trygve Holtebekk Prof. emer. Finn Ingebretsen Professor Gunnar Løvhøiden Professor Svein Messelt Assoc. prof. (Section leader) Eivind Osnes Professor John Rekstad Professor Anders Storruste Senior scientist Roald Tangen Prof. emer. Per Olav Tjørn Professor Trine Spedstad Tveter Research assoc. (NAVF)

2.2 Technical Staff

Eivind Atle Olsen Section engineer Jon Wikne Section engineer John Taylor Engineer ass.

6 2.3 Visiting Scientists

Dunja Sultanovitc on leave from University of Sarajevo.

2.4 Students

As of December 31,1992,13 graduate students (for the degree Cand. Scient.) and five post-graduate students (for the degree Dr. Scient.) were associated with the section.

7 Chapter 1

The Cyclotron

3.1 Operation and Maintenance

E. A. Olsen, J. Wikne, J. Taylor and S. Messelt The beam line has been modified to make room for a target station close to the cyclotron. This has made it easier to obtain the beam intensity which has been asked for in connection with the astatine production. The total beam time used for nuclear experiments in 1992 was 332 hours with 3He beam. The time used for isotope production for the nuclear chemistry group was 16 hours with protons and 85 hours with alpha beam. Approximately four weeks have been used for scheduled and two weeks for unscheduled maintenance.

8 Chapter 1

Data Acquisition and Analysis

4.1 Introduction

The data acquisition system at the Oslo Cyclotron Laboratory may be divided into two major components:

• A front-end system responsible for data digitalization, read-out and formatting. This system is based on a VMEbus with connections to CAMAC and NIM devices. • A rear-end system used for on- and off-line analysis. This system is based on a ND-5800 minicomputer. A UNIX workstation is connected to the ND-5800 through Ethernet.

The total acquisition system is shown in fig. 4.1, and a detailed description is given in the annual report for 1991.

Domino MC68020

Figure 4.1: Schematic view of the data acquisition system.

9 4.2 Configuration

Few changes were made during 1992. However, in October a new Sun Sparc- station 10 was acquired. The intention is that this computer, with VME interface still to be installed, should in time replace the increasingly obsolete ND-5800 computer. Also, the CAMAC pile-up rejection module (PUR) was installed, see a subsequent section. The service contract on the ND-5800 was terminated as from November 1, due to the unreasonably high cost, no longer to be justified by the computer's limited use. We are gambling that it will be possible to maintain the ND- 5800 at our own expense until its replacement is fully operative. a) Front-end VMEbus system with: CES FIC 8230 CPU, MC68020/68881, 2 MB DRAM VALET-Plus firmware 1 CBD 8210, CAMAC Branch Driver 1 NIM Interface 1 TSVME 204, EPROM socket card 2 VBR 8212, VME-VME link, receiver 1 VBR 8213, VME-VME link, transmitter 3 TPUs, Trigger Pattern Units

NIM ADC Interface System with: 16 Silena 7411/7420G ADCs

CAMAC system with: 4 Silena 4418/V ADCs 4 Silena 4418/T TDCs

Apple Macintosh SE with: VALET-Plus Bridge 1 20 MB disk drive b) Rear-end ND-5800 computer with: SINTRAN III operating system 20 MB memory, 384 kB cache memory 1 MF-VME DOMINO Controller 1 Internal 3-slots VMEbus 3 450 MB disk drive 1 70 MB removable cartridge 1 Floppy disk drive, high density 1 MT unit, 1600/6250 BPI 1 5 GB Exabyte cartridge tape unit 1 150 MB streamer tape unit 1 Ethernet connection, TCP/IP software

10 1 HP-7550A graphics plotter 1 Philips GP 300 printer 1 Genicom 340 line printer 1 Epson LX-80 printer 1 Interactive workstations, each with:

a) "DICO" video colour display, 8 colours, 384 lines each with 288 pixels, display controller and video memory in CAMAC. Another CAM AC module is used for cursor generation and colour trans- position from 8 to 4096 possible colours. b) CRT terminal

1 Tektronix 4612 video hard copy unit 30 Terminal connections via NET/ONE 1 X.25 connection, Coloured Books file transfer protocol 3 Local terminals 1 CAMAC crate

Apollo DN4500 workstation with: UNIX bsd4.3 operating system, X Windows MC68030/68882 CPU, 8 MB memory 1 350 MB disk drive 1 Cartridge tape, 60 MB 1 Colour monitor, 1280 x 1024 pixels 1 Ethernet controller, TCP/IP and NFS software 1 QMS PS-810 PostScript laserprinter

Sun Sparcstation 10-30 with: Solaris 1.4 operating system (BSD 4.1.3 UNIX), Open Windows SuperSPARC TMS390Z50 36MHz CPU with 36kB cache, 64 MB memory 1 SCSI mass storage expansion box 1 420 MB disk drive 1 1.8 GB disk drive 1 Colour monitor, 19", 1152 x 900 pixels 1 Ethernet controller, TCP/IP and NFS software 1 5 GB Exabyte cartridge tape unit

11 4.3 Acquisition and Data Analysis Software

SHIVA:

This is the main data-acquisition and on-line analysis program at the lab.

DAISY: Program controlling the front-end part of the sj item, normally operated from SHIVA. KELVIN: Program to manipulate large 2-dimensional matrixes. It contains 23 commands like: read, write, add, subtract, multiply, smooth, compress, project, cut, etc. In addition, the package contains more complex functions like - unfolding of Nal 7-spectnun. - folding spectra with Nal response function. - extraction of nuclear temperature from 7-spectra.

CSMA:

Cranked shell model with asymmetric nuclear shape.

DECAY: Calculates the 7-decay for a Fermi gas system. The lowest excitation region is simulated using experimental data. EMMA: Calculates E1, Ml, E2, Ml transition probabilities between single quasiparticle states from the RPC program (see below).

FIGEGA:

Extract first-generation 7-spectra from a set of unfolded spectra.

GAP:

Solves the BCS gap-equation.

HFBC: Hartree-Fock-Bogoliobov Cranking model based on Nilsson orbitals from the RPC program (see below). KINEMATIC: Calculates relativistic energy loss at a given scattering angle. Bethes formula. Straggling. Also available on IBM-PC and Mac.

12 PAW: CERN-developed Physics Analysis Workstation running on the Apollo.

Ge-spectrum manipulation program. Fast peak search, peak centroid and area estimation from observed data.

REDUC: Program for off-line data reduction on ND-5800. Accepts both Exabyte and STC magnetic tape as I/O devices.

RPC:

Rotor particle coupling model based on Nilsson orbitals.

PROPLOT: Plotting program based on the GPGS-F graphics package. Output on HP- 7550A pen plotter. Spectra stored on disc in Nordic format. Runs on the ND-120 part of the computer. PCPLOT: Subset of PROPLOT. Output on IBM compatible PC. Runs on the ND-120 part of the computer.

4.4 The CAMAC Pile-Up Rejection Module (PUR)

J. Wikne The PUR module described in last years annual report was completed, tested and integrated into the acquisition system during 1992 (ref.1,2). It proved a useful tool for its purpose in the experiment of May / June this year.

References:

1. J.C. Wikne A CAMAC 32-channel Pile-Up Detection and Rejection Module, Department of Physics, University of Oslo Report, UiO PHYS 92-28

2. J.C. Wikne A CAMAC 32-chaimel Pile-Up Detection and Rejection Module, Nucl. Instr. and Meth. (NIM), in press

13 Chapter 1

Nuclear Instrumentation

The main investment for 1992 was a new SparcStation 10/41, which will replace the old NORD-5800 computer at the Cyclotron Laboratory. The computers and the data acquisition system (DAISY) is described in ch. 4. In the next sections, an outline of the instrumentation projects are given.

5.1 The CACTUS Project

M. Guttormsen and S. Messelt

The CACTUS multidetector set-up was described in detail in the annual report for 1988. Thus, only a short description will be given. The CACTUS detector accommodates 8 AE-E telescopes, 28 Nal and 2 Ge detectors and is mounted on the 90° beam line of the Oslo cyclotron. The 28 Nal counters are fixed to the detector frame and have a distance of 24 cm to the target. In addition to the Nal counters there is space for 2 tie counters. At present we have two Ge-detectors with efficiencies of 49 an 72 %, respectively. The Si telescopes are mounted in a fixed frame of nylon placed within the target chamber. The frame has space for 8 telescopes at an angle of 9 = ±45° and at a distance of 4 cm from target. The target chamber can be removed from the centre of the Nal ball through the two remaining holes (32 holes in total). Beam focusing can be performed with a piece of quartz at the target place, where the beam spot can be monitored by a TV camera through a plexiglass window. The 5" x5" Nal(Tl) detectors (BICRON) are equipped with 5" PMT. The detectors aire shielded laterally with 2 mm lead and collimated with 10 cm lead in front. The solid angle of each detector corresponds to 0.5 % of Air. The front of the detectors are covered with a 2 mm Cu absorber. The particle telescope consists of a front and end detector. The front counter

14 21 4«

Figure 5.1: The SIRI detector seen perpendicular and along the beam axis. has a thickness of 150 fim Si and is manufactured by TENNELEC. The end counter is 3000 fim thick, and is of the Si(Li) type from the firm IN- TERTECHNIQUE. Both detectors have active area of 100 mm3 and can run at room temperature. An Al-absorber of 19 (im and a 4 mm thick Al-collimator are mounted in front of each telescope. The electronical set-up for CACTUS is based on fast ECL electronics. Both CAMAC and VME bus standards are applied.

5.2 The SIRI Strip Detector Project

M. Guttormsen, S. Messelt and J. Wikne In 1992 it was clear that the SIRI project would get funding by the Norwe- gian Research Council. The SIRI (Silicon Ring) system will be used in the study of nuclear behaviour as a function of temperature. It consists of an array of silicon particle telescopes for the detection of light particle emission. The telescopes will be placed inside the CACTUS detector, and thus the CACTUS/SIRI combination represents a powerful particle-7-coincidence set-up. The SIRI detector consists of 8 trapezes, each divided into 8 strips. A schematic view of the planed out-lay is shown in fig. 5.1. The detectors are located on a ring around the target, covering the angles between 30° and

15 30 ns multiplicity (x50mV) det 19 32 detectors det. 30 = SO ns <=o det 5 went pile-up on/off r reset /chip gate, computer energy, analog ready 1 in— H n n-« H s

hitpattern clock Leading edge fast logic signals from 0 0 preamplifiers are added to 0 1 multiplicity 1 1 common energy 0 1 threshold (OAC) Pile-up rejection 0 1 = 6|is common lime Energy and hitpattern are width multiplexed and read out by clock data common gain controll

Figure 5.2: In/out signals for the chip.

60° relative to the beam direction. The particle telescopes should stop at least 60 MeV a-particles, which means that the end detector should be at least 1500 fim thick. It is also important to stop protons in the telescope for the purpose of appropriate particle identification. We therefore aim on a thickness as high as 2000 /im, which represents a technological challenge. The front detector will be 130 fan. thick, so that a-particles of around 15 MeV can pass through the detector. The front and end detector have the same trapezoidal form and is to be sandwich mounted back-to-back. The detectors will be fixed on a ceramic plate, where bounding and cabling can be done. Furthermore, the detector will be mounted to a mechanical frame via the ceramic plate. Center for Industrial Research got autumn 1992 the commission to design the detectors and to perform pattern generation of 4 mask-layers. In the read-out part of the system, we will use a custom designed, monolithic chip (ASIC). The chip will be a general purpose chip, that can be applied also for other silicon balls (CHICSI, EUROBALL). Each chip will probably be designed to handle 32 silicon strip detectors. The in/out signals and the functions of the chip are indicated in fig. 5.2. The chip should give both good energy and timing signals. Generally, only one or possibly two (or three) detectors fire per chip. Therefore, the coincidence detected within the chip are handled using a summing technique of the logic timing signals. The time width for the overlapping pulses are set externally.

16 computer ready ^ (reset) ENERGY preamp shaper 10 ns 1 us

RESET LATCH

MULTIPLICITY other channels ns summing up to total multiplicity

a "LT •TJ- b b

c ~LT c pile-up no pile-up

Figure 5.3: The on-chip pile-up rejection.

The processing of the timing signals is a compromise in order to limit the number of cables out of the target vacuum chamber and to reduce the pin count of the chip. It seems like a complicating factor to make constant fraction discriminators (CFD) on every channel, and with individual readout for each detector. One might instead consider, with today fast computers, to correct in the off-line analysis the leading edge timing signal according to the associated energy pulse. An illustration of the chip circuit is shown in fig. 5.3. The computer ready signal resets latches and energy buffers, but not multiplicity and pile-up detection. This part of the circuit is always ready to take events. The inspection for pile-up is performed both before and after the event of interest. If two signals arrive within 2 fis, the corresponding latch will be reset (signals less than 100 ns apart can not be separated). Pile-up on/off has a fixed level, which is set externally for the specific experiment. The function set-latch gives the channel fired. The latch for other channels can not be set (only reset) after the multiplicity signal for the event is back to 0. The multiplicity signal is a linear sum of the logical signals from all detectors. The signal can be used to make multiplicity requirements or fast coincidences with other types of detectors. In this way, reset can be performed (the computer ready signal) at an early stage for bad events. The chip resets within 1 ns. The analog energy part stays always open, until reset is performed. In this way energies can be read out even without the presence of set-latch. The chips are planed to be finished at the end of 1993.

17 5.2 Gb exabyte 2.1 Gb disk

SparcStation 10/41 64 Mb memory 1 Mb cache, 320 Mb/s Real time, SVR4

NIM CAMAC ROCO

Figure 5.4: Rear-end acquisition system.

The data acquisition system has to be replaced in order to handle the high data rate, which is more that 10 times higher than earlier. The rear-end system is shown in fig. 5.4. The system is build around a SparcStation 10/41, with an interface (BiT3) to the VME crate where a single board computer takes care of the eventbuilder process. The SIRI system is planned to be installed in conjunction with the CACTUS detector in autumn 1994. Further details on this project is given in ref.1).

1. M. Guttormsen SIRI, A proposal for a multi-detector AE-E particle telescope Department of Physics, University of Oslo, UiO PHYS 92-21

5.3 The CHICSI Multifragment Detector

M. Guttormsen and the CHIC collaboration The CHICSI detector (CHIC collaboration) is a AE-E telescope system for the measurement of charged ejectiles produced in violent nuclear collisions. Of particular interest is the detection of intermediate mass fragments in

18 Figure 5.5: Tentative detector arrangement in forward direction. order to investigate the behavior of nuclear matter under extreme conditions. The telescopes will consist of a thin AE Si counter of ~ 10 pm, ir. order to measure heavy fragments with low kinetic energy (> 1 A MeV). The next AE detector will be of 300 (or 1000) fim. Finally, the end detector will be a scintillator (GSO probably) of 1 cm3 and with photodiode read-out. It might be slightly different detector configurations in different angles 9. The detector is intended for experiments at the CELSIUS storage ring. Thus, the operation in a storage ring environment requires special attention to the ultra high vacuum (UHV) condition and gas jet target arrangements. The instrument should be operational in conjunction with other detector systems. The basic geometrical constraints are a detector size of 1 cm3, all detectors have same size and shape and no detectors are closer to the beam than 5 cm. This leaves in principle only one possible geometrical solution. Figure 5.5 shows the forward part of this configuration. The telescopes are organized in 17 rings with 32 telescopes in each. All rings are almost identical except for the tilt angle of the telescopes which should be mounted perpendicular to the direction of the fragments at the particular angle. Some solid angle is lost in each ring since full coverage would require trapezoidal shaped detectors with different dimensions for different rings. For reasons of cost and flexibility we consider it to be so attractive to have identical detectors everywhere, that we accept the resulting loss of solid angle. Rings

19 can be moved to other angles by simply replacing the support ring which determines the tilt angle. The read-out solution is based on the construction of special read-out chips, similar to the case for SIRI. These will handle the telescope read-out and low level trigger functions from a number of telescopes simultaneously. The same chip can be used for 3 and 4 element telescopes. In the former case part of the circuitry on the chip will be redundant. The chips will sit inside the vacuum and act as signal multiplexers. These circuits will be a combined analogue/digital device. The chips will be fabricated using standard 2/xm CMOS processing technology. This process gives devices with good analogue and digital performance a; a reasonable cost. The chips will be read out under computer control using control-cards that speed up the data acquisition by inhibiting null-events from being converted by the ADC, but satisfying the criteria that no relevant information about an event is discarded. Signals fr om all particles that impinge on a telescope that are associated with an event which fulfils the trigger criteria, are recorded. More details on this project is given in the proposal1).

1. CHICSI version II, A proposal for a multidetector AE-E particle telescope (ed. M. Guttormsen) Department of Physics, University of Oslo, UiO PHYS 93-01

20 Chapter 1

Experimental Nuclear Physics

6.1 Introduction

The experimental work at the cyclotron has been devoted to the study of nuclear structure at low spin and high excitation energy. The method is based on measuring charged particles from transfer reactions in coincidence with 7-rays. In this way 7-ray spectra at various nuclear excitation energies can be produced. The project is of general physical interest: To what extent can one ascribe statistical properties as temperature and entropy to a microscopical few- body system? It is well known that the low energy part of nuclear excitations is determined by the orbitals occupied and the collective degrees of freedom. However, a few MeV above the yrast line one is bound to use statistical concepts. It is an open question if chaotic particle motion can be produced in hot nuclear matter. The group has found that the if-quantum number may serve as a fingerprint for the degree of order in deformed nuclei. Investigating how the 7-decay routes is governed by A" is a very promising approach to these problems. In order to increase the efficiency of the particle-7 coincidences further, the design of the SHU multidetector system has been initiated (see ch. 5.2). The combination of SIRI and the present Nal-array (CACTUS) will be most powerful in the study of nuclear properties as a function of temperature. The contributions during the year in the study of nuclear behaviour at moderate temperatures are presented in ch. 6.2. The work on rotational and high-spin states has also continued in 1992. The experiments were carried out at the Niels Bohr institute in Risø, KVI Groningen and at ISOLDE, CERN. The main topic of this research is the behaviour of nuclei exposed to rapid rotation. In particular, single-particle

21 structures and pairing-correlations have been studied as function of rotational frequency. The growing information on excited bands in the second minimum (superdeformed bands) is also of great interest. The field is in strong development, and powerful detector systems with Compton- suppressed Ge-detectors are used. We participate in the NORDBALL collaboration, which is a detection system with 20 Compton-suppressed 7-ray spectrometers. Experiments within the field of high-spin states are presented in ch. 6.3. The group participate also in experimental intermediate energy heavy ion physics through the CHIC-collaboration. There are many topics of fundamental nature that we want to investigate in this project. We wish to find out whether substantial compression of nuclear matter can be achieved in heavy ion reactions, to learn about the nuclear equation of state far away from the ground state, to find out whether a liquid/gas phase-transition takes place during the decompression phase and whether the multifragmen- tation processes are connected to such critical behaviour of nuclear matter. A new multidetector system CHICSI (see ch. 5.3) is planed to be built and placed at the CELSIUS storage ring in Uppsala. With the advent of ultra-relativistic heavy-ion collisions in the laboratory in 1986 (CERN and Brookhaven), a new interdisciplinary field has emerged from the traditional domains of nuclear and particle physics. What may make this field particularly interesting is the prediction of QCD that at high energy densities matter is predicted to undergo a phase transition to an entirely new state, the quark gluon plasma (QGP). The nuclear physics group has entered this new field. The investigations are conducted within the CERN collaborations NA36, WA94 and WA97. The work has focused on the measurement and study of the strange particle production in the nuclear collisions as the enhancement of such production is seen as a possible signature of the creation of the quark gluon plasma. In 1994 a 160GeV per nucleon lead beam will be available in CERN. The WA97 collaboration will participate in these future Pb+Pb experiments. In relativistic collisions between such truly heavy ions the larger volumes, the higher energy density and the increased lifetime of the reaction zone will considerably improve the possibility of making the phase transition to the QGP. The experimental work on high and intermediate energy nuclear physics is described in ch. 6.4.

22 6.2 Nuclear Properties at Moderate Temperature

6.2.1 Extraction of Multiplicity Distributions

L. Bergholt, M. Guttormsen, J. Rekstad and T. Tveter The centroid and the shape of the 7-multiplicity distributions are sensitive indicators of changes in the 7-decay pattern as a function of excitation energy. Using the detector array CACTUS, we record multiple-fold a-7-coincidences. CACTUS is particularly suitable for this purpose, as it consists of 28 Nal counters with a total 7-efficiency of approximately 10%, and 8 particle telescopes with a total solid angle of 3%. The occurrence of Jb-fold events, defined as events where 7-rays simultaneously are detected in k 7-counters, contains information about how the multiplicity distributions change with excitation energy.

The probability Pk for observing a Jb-fold event is connected to the multiplicity distribution p(M) through the relation1):

^ = (JO + ^yn* + + . . . (6.1) where

yn = ln(l - (JV - n)fi),

N being the total number of 7-detectors and 0 the effective solid angle of each detector. (M) is the average multiplicity, cr and 5 are the standard deviation and the skewness of the distribution, respectively. The quantity (G„) is the probability for at least (N—n) given 7-counters not to participate in an event:

(Gn) = X>(M)[1 - (AT - n)n]" M -t(:)( J)"™-

In general, the series in eq. (6.1) converges rapidly. Since (Gn) is a linear combination of the experimental quantities (Pk), and yn ideally is a constant for a given detector array, the parameters

23 drop in multiplicity just above B\n is due to evaporation of a single neutron, and similar drops are observed each time a new neutron channel becomes energetically available. The maxima in the standard deviation spectrum, coinciding with the drops in multiplicity, are due to competition between neighbouring isotopes, one with high and one with low excitation energy. The resulting multiplicity distribution, being a superposition of two components with different centroids, will exhibit a large width.

: "VbCHe.axn)"*"Yb n c R B|n a> D2n f O

j., 1 \ V-'-V""-'- * k v'fb , l 7 Average 7-multipficity Standard deviation ** " VH j . . i • • •• 1 ^ 1 • 40 35 30 25 20 15 10 5 0 Excitation energy (MeV) Figure 6.1: Average multiplicity and standard deviation from the reactions 163Dy(3He,aæn)l62~*Dy and lwYb(3He,a»n)I7a—Yb.

Information regarding the neutron energy distributions may be extracted from the average multiplicity and the standard deviation as functions of excitation energy. In particular, the spread in neutron energies is related to the width of the peak structures in the standard deviation spectrum. The neutron energy distribution contains information about the nuclear temper- attire, and therefore about the thermalization of the nucleus. The analysis so far3) indicates that the nucleus may not be completely thermalized when the neutrons are evaporated, but more analysis has to be done before we can draw any conclusions.

References:

1. W. Ockels, Z. Physik A286 (1979) 181 2. Nuclear Physics Group Annual Report 1990, Dept. of Phys. Report,

24 Univ. of Oslo 91-11 (1991) 31 3. L. Bergholt, Cand. Scient. Thesis, Univ. of Oslo (1992)

6.2.2 Spin Population in the l62Dy(3He,a)mDy Reaction

S. Siem, L. Bergholt, M. Guttormsen, J. Rekstad and T. Tveter We have studied the spin population in the 163Dy(3He,a)l6lDy reaction with a beam energy of 45 MeV. The method employed is described in ref.1). By means of the coincidence technique, the 7-rays from various daughter nuclei are isolated. Examples of Ge-spectra from 160Dy and 158Dy are shown in fig. 6.2, corresponding to the evaporation of one or three neutrons, respectively.

7 Ge-soectru'o fo- Dy « Ge-spectrum for "*Dy

"^AwlllL.i 100 200 300 400 S00 600 700 100 200 300 400 500 600 700 y-cergy (keV) y-energy (keV) Figure 6.2: Germanium spectra for 160'lS8Dy.

The peaks correspond to different rotational transitions along the yivst lines in ls8,160Dy. From the 7-line intensities we have deduced the sidefeeding into the different spin states. In table 6.1 the intensities and sidefeeding strength are listed. The sidefeeding gives us an idea of the spin population1) in the (3He,a) reaction at different energies (Q-values). Plots of the sidefeeding as a function of spin are shown in fig. 6.3. The figure shows a shift towards higher spins from l60Dy to 1S8Dy in accordance with observations in other reactions. A detailed investigation of the data from the 163Dy(3He,a)161Dy reaction is in progress.

References:

1. T.S. Tveter et al., Nucl. Phys. A516 (1990) 1

25 l60Dy 158Dy

Transition Intensity Sidefeeding Intensity Sidefeeding 4+ 2+ 248(17) 101(22) 790(30) 131(42) 6+ —. 4+ 147(14) 85(17) 660(29) 235(38) + 8+ 6 62(10) 50(18) 425(26) 175(40) 10+ — 8+ 12(15) 12(15) 250(30) 144(37) 12+ 10+ 106(21) 51(33) 14+ — 12+ 55(25) 55(25)

Table 6.1: Relative intensities of each rotational transition and sidefeeding into the ground bands for both nuclei.

.„««,.> Spin-distribution in Dysprosium 160 ln"mi.y Spin-distribution in Dysprosium 158 I I I 250 M j H—1—^——h~ T

i i m i

•j 200 00 » jll^—j. r— I • I I I I II spu> É l<>» •'«pin i- «. Id. 12. ». Figure 6.3: Spin distribution in 160 158Dy extracted from the sidefe^ding into the ground band states.

26 6.2.3 Nuclear Temperature in 3He Reactions

A. Mlonyeni, L. Bergholt, M. Guttormsen, G. Løvhøiden and J. Rekstad This work urns to explore aspects of the so called hot-spot theory. The experiments were performed with 30 and 45 MeV 3He particles delivered by the MC-35 cyclotron at the University of Oslo. A scattering chamber set-up was used, containing two movable particle telescopes and one fixed monitor detector. The movable counters covered the angles 6 between 22.5° and 315.0° in steps of 22.5°. The reactions studied were (3He,a) and (3He,d) with targets of 13C, 27A1, nalCu, l72Yb and 198Au. At present the a- and d-spectra have been analysed. Figure 6.4 shows the a-spectra from ytterbium in angles of 112.5°, 135.0° and 157.5°.

\)=112.50

Itod^UJJJ,,, U I III lill II. i I i i 400 600 800 1000 1200 1400

F ill III—I ii ii • •••••inaiMimiiiiiiMiiiiiMiiinii mun • » i. I . • 400 600 800 1000 1200 1400

400 600 800 1000 1200 1400 Figure 6.4: Preliminary a-spectra from the reaction (3He,a)l72Yb. The energy dispersion is .04 MeV/ch.

The data will be systematically studied as a function of mass number and excitation energy, and we will focus on the competition between the preequilibrium and the compound processes. The work is in progress.

27 6.2.4 Level Densities in 162Dy

L. Henden, L. Bergholt, M. Guttormsen, J. Rekstad and T.S. Tveter In this work we have investigated the level density up to about 8 MeV of excitation energy in 162Dy. Usually the level density is described by the statistical Fermi gas model, which give a reasonable agreement with the experimental level density over a wide energy region. A particularly interesting phenomenon is the transition from the pairing correlated regime in the lower excitation regions to the Fermi gas regime. One way to investigate this transition is by detailed studies of the level density over the transition area. Our purpose is to determine the level density by means of the first generation 7-rays following the l53Dy(3He, a)l62Dy reaction. The method for extraction of first generation 7-ray spectra is described in a previous paper1). The experiment was carried out with 45 MeV 3He-particles delivered by the MC-cyclotron at the University of Oslo. The 7-rays were recorded in the multidetector system CACTUS2). The detector arrangement consisted of 28 Nal detectors and 2 Ge detectors in an outer ball, and a ring of 8 Si telescopes for particle detection placed inside. The energy distribution of the first generation 7-rays is given by

P(E„ Ex) oc Eya(Ex - Ey) (6.3) Here n is the 7-exponent which depends on the muitipolarity A and the contribution from GDR (giant dipole resonance). The level density p is given by3)

P(U) = C-j-2e^, (6.4) where a is the mass dependent level density parameter, C is a constant and U = Ex- ZSpair - .

The first generation matrix P(£7, Ex) has been used to determine average values for the parameters a and n, following the procedure described in ref.4). For the excitation region from 3 to 8 MeV the best fit was obtained with n=4.5±0.4 and a=(18.0±1.5) MeV"1. Figure 6.5 shows examples of the level density spectra in 162Dy obtained by means of eq. (6.3). It is evident from these spectra that the level density grows exponentially with excitation energy in the region between 3 MeV and 6 MeV. Above 6.5 MeV this method gives unreliable results, since the 7- rays with energy less than 1.5 MeV are essentially non-statistical in nature. Correspondingly only few transitions appear with the highest 7-ray energies. Therefore, each spectrum in fig. 6.5 displays a certain energy window where the level density is rather accurately measured with regard to the statistics. The spectra are compared with theoretical level density given by eq. (6.4), and with the level density parameter found to give the best overall description of the whole 7-spectrum. This theoretical level density is shown as full drawn lines fig. 6.5. It gives a very good fit to the energy region above 3 MeV of excitation. Below 3 MeV the experimental level density is larger

28 0123456789 10 0123456789 10

Q.10* E,= 7.56 -

10' 1 ru « i; 10 r f 1

-1 10 1 -2 1 10 I.I J l„ ! —i— 3456789 10 0 123456789 10

ENERGY(MeV)

Figure 6.5: The level density (ln/p in arbitrary units) as a function of excitation energy.

29 than the theoretical one. This information is of importance for calculations of decay processes feeding this region, since the branching ratios depend essentially on the level density. The theoretical explanations for this discrepancy is not trivial since the transition from a superfluid regime to a Fermi gas regime is not accurately described. It is however interesting to notice that the large level density in the region between 2 MeV and 3 MeV of excitation is in accordance with the expectations of an collections of states due to the pairing correlations. This region may therefore be a candidate for the phase transitions region between superfluidity and Fermi gas.

References:

1. M. Guttormsen, T. Ramsøy and J. Reks'.ad, Nucl. Instr. Meth. A255 (1987) 518 2. M. Guttormsen, A. Atag, G. Løvhøiden, S. Messelt, J. Rekstad, T.F. Thorsteinsen, T.S. Tveter and Z. Zelazny, Phys. Ser. T32 (1990) 54 3. A. Richter, Nuclear Spectroscopy and Reactions B (Edited by J. Cerny), p. 343, Academic Press, New York (1974) 4. M. Guttormsen, A. Atag, K. Klungeland, S. Messelt, T. Ramsøy, J. Rekstad, T.S. Tveter and Z. Zelazny, Nucl. Phys. A531 (1991) 370

6.2.5 Excitation Regions in 161Dy Feeding the Isotopes 161-*Dy

E. Koksvik, L. Bergholt, M. Guttormsen, J. Rekstad and T.S. Tveter This experiment was performed 1992 in order to investigate the decay properties of 16lDy after the reaction 162Dy(3He,a). The standard CACTUS setup was used and distributions of singles and coincidence a-particles spectra were extracted. Our main goal is to study the gamma/neutron decay to the various dysprosium isotopes. The neutron as well as the 7-ray energy distributions depends on the density of available final states. Our calculation is founded on an expression describing neutron decay based on level density. For the level density (number of levels/MeV) we assume the following formula for a certain spin J, parity tt and massnumber A

p(£x, /*, A) = p,tMt + PFermi + Pother- (6.5)

The function pyrM, is the level density of the yrast states. It is nonvanishing for the yrast level having proper spin/parity I' and is described by a 8- function in Ex. The Fermi level density is described by

PFem>i{E ,r,A)= lLt±^A2'3(rT+ T)-2exp2VtfJ , (6.6) x «4

30 where T = ^(1 + y/l + 4 aU). (6.7)

The main parameter for pFrniu is the level density parameter a. In the rare earth region a takes values between 10 and 25 MeV-1. The intrinsic excitation energy U is defined according to spin and the type of system considered U{I) = EX- EJIMt(I) - fipair , (6.8) where Ejrsut(I) is the excitation energies of the yrast states and EpKir is the pairing energy defined as 0, A or 2A for odd-odd, odd-A or even-even nuclei, respectively. An out-line of the model was given in the annual report for 1991. The experimented data will be compared with theory in order to obtain information on spin distributions and the level density.

6.2.6 Transferred Angular Momentum in the (3He,a) Reac- tion

M. Guttormsen, L. Bergholt, F. Ingebretsen, G. Løvhøiden, S. Messelt, J. Rekstad, T.S. Tveter, H. Helstrup and T.F. Thorsteinsen The (3He,a) reaction changes its nature as a function of ejectile energy. In the very low excitation energy region the cross section is described by the dircct pick-up process, which depends on available high-,/' neutron orbitals. At higher excitation energies, where the reaction appears more in the interior of the nucleus, the incoming 3He and ejected a ions might excite other reaction modes. This gives origin to local heating, whicii often is referred to as preequilibriutn. The third possibility is that the entrance and the exit channels are uncorrelated. In this . vpe of compound reaction the a-particle is evaporated from a nuclear system in thermal equilibrium. The aim of the present study is to investigate the importance of these three mechanisms in the 163Dy(3He,a) reaction. The experiment was performed at the Oslo Cyclotron Laboratory with a 45 MeV 3He beam. The selfsupporting 2.0 mg/cm2 thick 1G3Dy target was isotopicaUy enriched to 97 %. The coincidences between -y-rays and a- particles were measured with 2 Ge detectors and 8 AE-E particle telescopes at an angle of 45°, respectively. The experimental method is based on studying the 7-ray side-feeding of the ground band states of dysprosium isotopes after the l63Dy(3He,aa;n)162~*Dy reaction with x = 0, 2 and 4. The side-feeding 5(J) is determined from the 7-intensities by 5(7) = J,(J — / - 2) - J,(J + 2 — I). In order to extract the distribution of the transferred angular momentum P(J) from the (3He,o) reaction itself, we have to correct for the spin AI removed by neutrons and statistical 7-rays and the density p(J) of available spins in the target nucleus. We include these effects by P(I) oc S(I -

31 Compound

Ol 1 1 1 1 1 1 1 0 5 10 15 20 25 30 35 Excitation energy (MeV)

Figure 6.6: Comparison of experimental and theoretical average spin transfer in the 163Dy(3He,a)162Dy reaction

AI)/p(I). Here, we have used the Fermi gas model prediction1) giving I I v 1 />(/) oc (21 + 1) e- ( + f "' t where a is the so-called spin cutoff parameter. The applied spin shift A/ has been theoretically estimated3) to 0.5 h as contribution from the 7-cascades and 0.5ft from each neutron evaporated. The cutoff parameter is deduced from the expressions given in ref.1) and increases from 5.1 to 9.5 for the excitation region from 5 to 38 MeV. In fig. 6.6 is shown a comparison between the experimental values and estimates of the average spin transfer expected within the three scenar- ios described above. The preliminary analysis indicates that the (3He,a) reaction undergo a transition from the direct pick-up type of reaction at 5 MeV to a preequilibrium type at 30 MeV.

References:

1. A. Richter, Nuclear spectra and reactions 6, ed. J. Cerny (Academic Press,1974) p.346 2. T.S. Tveter et al., Nucl. Phys. A516 (1990)1

32 6.2.7 Gamma-Ray Branching and the K Quantum Number in Even-Even Rare-Earth Nuclei

T. S. Tveter, M. Guttormsen and J. Rekstad The 7-decay pattern observed after low-energy neutron capture suggests that the K quantum number still is partially conserved up to Ex « 8 MeV (ref.1,3)). An interesting question is whether K selection effects may be traced even higher up in excitation energy. A suitable probe for such an investigation might be the 1 MeV peak seen in low-resolution 7-spectra from even-even deformed rare earth nuclei3) at low spin. This spectral feature actually consists of a number of discrete transitions from vibrational and low-lying two-quasiparticle bands at Ex w 1-2 MeV (the so-called vibrational region) and down to the ground band. The location of the peak is mainly determined by the edge in the level density found at EX(I) « EyTatt(I)+A. A strong correlation has been found between the K values of the various bands and their relative contributions to the peak. The decay pattern is easily accounted for by K selection rules: The high- K part of the population, which is not allowed to feed the K = 0 ground band directly, will preferably decay via the lowest-lying excited bands with appropriate K values. No such hindrance exists for low-if excited states, for which decay paths bypassing the vibrational region are open. Hence, the intensity of the 1 MeV peak should reflect the K distribution populated by the reaction. We have extracted the fraction PiMev(-EJ) of the decay cascades including such an 1 MeV transition as the last step down to the ground band, after 3 1 he ( He,a) reaction at Et,eam = 45 MeV. A clear reduction in the 1 MeV psak intensity is observed with increasing initial excitation energy. The probability for decaying via the vibrational region starts at 60 - 90% at the lowest excitation energies (£* w 1-4 MeV), and decreases gradually with rising temperature, stabilizing at about 30 - 35% for E'z > 20 MeV. This lower limit is tentatively identified with the amount of 1 MeV radiation solely due to the step in the level density function. A significant surplus of 1 MeV strength relative to this reference value, possibly suggesting partial survival of the K quantum number, is observed as high up as E\ as 10 - 15 MeV. The average spin introduced rises significantly with the energy transfer in the (3He,a) reaction1). It is possible that plain Coriolis mixing due to this spin increase is partly responsible for the decline of the function Piuev{E*). Besides, multiple decay steps will at least to some extent bring the K distribution closer to the statistical level density p(K). Hence, it is not entirely clear whether the 1 MeV peak represents a valid measure for the temperature dependence of the K mixing at the highest initial excitation energies. In order to obtain more quantitative information about the relationship between the 1 MeV peak intensity and the degree of K mixing in the initial state, we are trying to simulate 7-decay in (EX,I, K) space using the decay

33 probability expression:

- E*,Ij,Kf) « E-piElJtiKtmiuKi.ItiK,), (6.9) nsing various input spin and K distributions. The level density p(E£, If, Kf) s is given by the formula of ref. ). Below Ex as 2 MeV, the empirical level structure has been employed. The factor /(/<, Ki,Ij,Kj) represents various K hindrance conditions. Preliminary results, obtained by subtracting underlying statistical background from the 1 MeV peak structure in the simulated 7-spectra, yield approximately the asymptotic value P1Mev « 30 - 35% in the limit of total K mixing, while a high degree of K conservation is necessary in order to reproduce the peak intensity obtained at low excitation energies.

The analysis is in progress.

References: 1. J. Rekstad, T. S. Tveter and M. Guttormsen, Phys. Rev. Lett. 65 (1990) 2122 2. J. Rekstad, T. S. Tveter, M. Guttormsen and L. Bergholt, Phys. Rev. C, in press 3. T. S. Tveter, M. Guttormsen and J. Rekstad, to be published 4. T. S. Tveter, M. Guttormsen, J. Kownacki, J. Rekstad and T. F. Thorsteinsen, Nucl. Phys. A516 (1990) 1 5. A. Bohr and B. R. Mottelson, in Nuclear Structure, Vol. 2 (Benjamin, 1975) p. 38

6.2.8 The K Quantum Number and the Decay of Neutron Resonances

T. S. Tveter, J. Rekstad, M. Guttormsen and L. Bergholt The order-chaos transition predicted in heated nuclei is believed to imply complete mixing of quantum numbers related to the mean-field picture and the intrinsic nuclear coordinate system, such as the spin projection K on the nuclear symmetry axis. The degree of K mixing may be utilized as a probe for investigating the amount of disorder in the system: In the case of sparse configuration mixing and approximate K conservation, the 7-decay from a given eigenstate will essentially obey the selection rule A/if < A, A being the multipolarity of the transition, final states within a limited range of K values will be preferred. An initial state with extensive configuration mixing is composed by a large variety of components with different K values through which 7-decay may take place, and a wide range of final state K values can be reached without getting into conflict with the selection rule.

34 In two recent works1,2), we have explored the 7-decay properties of thermal and 2 keV neutron resonances in 168Er and 178Hf, reanalyzing the data from refs.3'4), and collecting supplementary information from refs.5'6). Capture of «-neutrons in the target nuclei 16TEr and 177Hf, having K* equal to 7/2+ and 7/2", respectively, populates excited states with spin I = 3,4, with opposite parities in the two product nuclei, and in the case of K conservation, with K values 3 or 4. The primary 7-decay of these levels, located at Ex ss 8 MeV, f> a number of well-established states at low excitation energy [Ex ~ 0 - 2.5 MeV) has been studied in detail. We have corrected the experimental transition probabilities for 7-energy, spin and parity dependence, introducing the dimensionless relative reduced transition probability x. We have limited the ensemble to final states having well-defined K values: Among the low- K final states, only those belonging to bands without significant Coriolis coupling induced energy staggering are included in the analysis. Details of the analysis are given in ref.2).

Average relative reduced transition probabilities {x)p and (x)A have been calculated for forbidden (Kf = 0,1) and allowed transitions (Kf =2-5). The corresponding hindrance factors (x)F/(x)A are 0.54 and 0.85 for thermal and 2 keV neutron energies, respectively. The distributions of relative reduced transition probabilities x are displayed in fig. 6.7. The terms "incl. / excl. doublets11 refer to whether transitions feeding different final states but lying too close in energy to be resolved experimentally, have been taken into account in the analysis or not. Our discovery has met strong opposition from Barrett et al.7), who obtained results different from ours when attempting to redo the analysis described above. The controversy is probably mainly due to our use of a more comprehensive level scheme for 168Er s), and our choosing the lowest transition intensities in two cases where the numbers tabulated in ref.3) and ref.6) disagree. After a critical recheck of our calculations, we still find it justified to maintain our previous conclusion about a significant apparent hindrance of transitions into "forbidden" final states. However, the hindrance factor estimated is not large, and alternative interpretations have been suggested, as discussed in ref.8).

References:

1. J. Rekstad, T. S. Tveter and M. Guttormsen, Phys. Rev. Lett. 65 (1990) 2122 2. J. Rekstad, T. S. Tveter, M. Guttormsen and L. Bergholt, Phys. Rev. C, in press 3. W. F. Davidson et al., J. Phys. G7 (1981) 455 4. A. M. I. Hague et al., Nucl. Phys. A455 (1986) 231

35 168,. 178,,, Er and Hf

15-

Thermal Thermal excl. doublets incl. doublets 10- 10- p =0 59 p = 0.59 fii = 1.10 A = 1.10

5 - X 5 - X

xln i i ta 0 12 3 4

15- 15-

ARC 2 keV incl. doublets 10- 10- p = 0.89 ^ = 1.05

5- å

Figure 6.7: Distributions of relative reduced transition probabilities x. Data from the two nuclei 1G8Er and 178Hf are added.

36 5. W. F. Davidson et al., Can. J. Phys. 62 (1984) 1538 6. W. Michaelis et al., Nucl. Phys. A150 (1970) 161 7. B. R. Barrett et al., Phys. Rev. C45 (1992) R1417 8. T. S. Tveter et al., Dept. of Physics Report 92-09, University of Oslo (1992), p.39.

6.2.9 Activities at NBI: Selective Studies of Hot Rotating Nuclei by Means of the Giant Dipole Resonance

J. J. Gaardhøje, A. Atac, A. Bracco, F. Camera, B. Herskind, W. Korten, A. Maj, M. Mattiuzzi, B. Million, M. Pignanelli, T. Ramsøy, G. Sletten, T. S. Tveter and Z. Zelazny During the later years, giant dipole resonance (GDR) radiation has been extensively utilized as a probe for investigating the properties of hot rotating nuclei1,2). The GDR, a high-frequency collective vibration of neutrons against protons, may be built upon any nuclear state. Due to nucleon-nucleon collisions, the GDR is strongly damped, mixed with other compound states and spread out over a wide energy interval. The eigenstates of a highly excited nucleus consist of numerous components, which may be divided into two groups: "normal" configurations, which decay through particle emission, and configurations including a GDR vibration, -'hich in addition may decay by emitting a high-energy 7-photon. The dominant decay mode for a hot nucleus is neutron emission, and GDR 7-ray emission only takes place in a fraction ss 10"3 of the cascades. The probability of high-energy 7-ray emission increases with temperature, and GDR photons are preferably emitted early in the cascade, while low-energy statistical 7-rays (Ey < Bn) are almost exclusively found only at the end of the cascade, when neutron emission is no longer energetically possible.

Many of the properties of GDR radiation may be understood by considering the vibrational motion as a superposition of three separate components, each along one of the three principal axes. The vibrational frequency of each component is roughly inversely proportional to the length of the corresponding principal axis. Accordingly, nuclear deformation will give rise to a splitting of the GDR energy distribution into different resonance peaks. The width of each component is related to the strength of the damping into other compound states. The angular distribution may be explained by regarding each component as a classical dipole antenna with its characteristic doughnut-shaped radiation pattern in space. The observed anisotropy as a function of energy will then depend both upon the nuclear shape and the orientation of the rotational axis in the intrinsic nuclear coordinate system.

Due to its ability to compete with particle decay at high Ex and the properties of the energy and angular distribution, the GDR radiation represents

37 a unique probe for exploring a wide variety of nuclear phenomena as functions of spin and temperature. Topics of great current interest are shape transitions, shape and orientation fluctuations and time constants of various processes. Recently, Sn isotopes (A « 110) and deformed rare earth nuclei (A « 160 - 175) at moderate excitation energies and spins (Ex < 100 MeV, I < 60 ft) have been studied intensively at the NBI Tandem Accelerator Laboratory. An overview of experimental methods and physical questions addressed is given below. The GDR 7-spectra seen experimentally are averaged over all spins populated and over all excitation energies, from the Ex at which the compound nucleus is formed and downwards. Due to the triangular shape of the fusion cross section

38 Helena

Figure 6.8: The present experimental setup at NBI, including the 8 large BaF3 HECTOR detectors and the HELENA multiplicity filter. crystal. The latter problem is solved by continuously monitoring the gain of each detector by injecting a constant amount of light from a LED (Light Emitting Diode) source into the crystal fts 10 times per second and record- ing the amplitudes of the resulting electronic signals as for normal 7-rays. These numbers are later used for off-line gain correction. Selectivity in spin is obtained by utilizing the fact that for the HELENA filter with 38 crystals, each fold measured corresponds to a reasonably narrow part of the total multiplicity distribution, with a well-defined centroid. When the total multiplicity distribution is known, the partial multiplicity distributions for each fold can easily be calculated on the basis of empirical information about the HELENA efficiency and cross-talk probability3). Since most of the 7-rays emitted in a decay cascade following a heavy-ion collision are E2 rotational transitions along or in the vicinity of the yrast line, the multiplicity is approximately proportional to the initial spin. By generating a fold-7-energy matrix, one can project out 7-spectra corresponding to narrow spin intervals. By excluding the lowest folds, one also gets rid of contributions from compound nuclei decaying by fission: The fission fragments are produced with low spin, since most of the angular momentum of the compound system is transformed into relative kinetic energy of the fragments.

Selectivity in energy is achieved by means of an energy differential method aimed at extracting the first-generation GDR spectrum4). Neighbouring isotopes and are produced at slightly different excitation energies

39 E'z and El - Bn - (En). The difference in Ex equals the average energy removed by the emission of one neutron from the nucleus AX. The corresponding total 7-ray spectra measured for matched spin intervals are called f(Ey) and g(Ey), respectively. The method is based upon the assumption that the decay pattern from a given excitation energy is independent of the mode of population, that the spread in neutron energy is small and that the probability for 7-ray emission at high T is small, so that each cascade can be assumed to contain no more than one 7-ray sent out above the neutron sep- aration energy. With these conditions fulfilled, the spectrum g{Ey) will be identical to the second- and higher-generation part of the spectrum f(Ey), containing 7-rays emitted at Ez < E'x - Bn - (En). The spectra f(Ey) and £[(£7) are normalized by requiring that the number of statistical 7-rays (Ey < Bn) per energy interval shall be the same in the two spectra. The difference spectrum h(Ey) will then consist of primary high-energy 7-rays emitted as the first step in the cascade starting at Ex - E\.

10»

10«

103

102

CO 101 G 3 10« O JK lSZYb-'S'Yb O 103

102 : f"

10>

10» SO 7 5 10 0 12 5 ISO 17.5 ZOO 22 5 E? (MeV| Figure 6.9: Illustration of the energy differential method, applied to the nuclei 162161Yb. The figure is taken from ref.1).

The experimental data are then compared with statistical model calculations. The program CASCADE5) simulates the total statistical decay of the excited, thermalized compound nucleus through particle and 7-emission. For each decay step, the usual statistical decay rate expressions are used together with the initial population matrix in (J\T, Z, Ex, I) space to calculate the final population matrix, which then serves as input to the next step. Each time 7-decay from an initial to a final cell in population space is calculated, the theoretical 7-spectrum is incremented at the corresponding Ey. The 7-decay rate as a function of 7-energy is expressed as:

2 I\(N, Z, E'x, I, - N, Z, El, I,) a E y, I,) (6.10)

where the photon absorption cross section

40 justable parameters 5, F, Ei, Ei, rt, r2, which will be explained below: r e"1 r E3 ^GDR(Ey)

In general, CASCADE is combined with a fitting procedure which involves the following steps: At the beginning of each iteration, a set of parameters (5, F, Eu E2, Ti, r2) are chosen, and a theoretical 7-spectrum is calculated. This spectrum is then folded with the detector response function, the result is compared to the experimental data, and the deviation x2 between theoretical and experimental points is calculated. If the fit is satisfactory, the iteration procedure is terminated at this point, if not, a new parameter set is selected according to a certain algorithm, and the procedure is repeated. The set giving the best description of the experimental data may finally be given a physical interpretation:

The overall strength S is related to the competitiveness of GDR radiation relative to other decay modes. The relative weighting F of the two Lorentzians determines whether the deformed nucleus is prolate or oblate, while the resonance energies Ex and E2 defines the energy splitting of the GDR and thereby the magnitude of the deformation. The widths and T2 of the two components are connected to the coupling of the GDR to other states and to fluctuations about the most probable shape. For mid-shell rare earth nuclei, which at low temperatures are prolate due to shell effects and rotating collectively, a transition to an oblate, non- collectively rotating shape is predicted at some tens of MeV. Here the shell effects are expected to vanish, the Fermi surface growing so diffuse due to thermal excitations that its exact location relative to the single-particle orbitals becomes unimportant. This transition has been observed in several nuclei, and the critical excitation energy varies with mass number6). Recent experiments producing neighbouring Dy and Yb isotopes at slightly different excitation energies aim among other things at pinpointing this transition in the (EX,I) plane by means of the selection techniques described above. Another topic which is currently being intensively explored is the nature of the fluctuations of the nuclear shape and orientation. Shape fluctuations influence the energy splitting and the width of the Lorentzians, and therefore both the energy spectrum and angular distribution. On the other hand, orientation fluctuations, where the nuclear spin axis is tilted with respect to the intrinsic coordinate system due to single particle spin contributions, do not change the relative length of the principal axes and affect the angular distribution only. The observed distributions must be described as weighted averages over all possible shapes and orientations, which occur with probabilities approximately proportional to e~FlT. Here F is Helmholtz* free energy at the temperature, rotational frequency, deformation and spin vector orientation of interest. The weighting function depends upon the ratio of two time constants: the typical time elapsed between leaps in deformation- orientation space and the time needed for damping of the GDR.

If the fluctuations are slow relative to the damping, the shape and orien-

41 tation can be considered static while the vibration couples to the normal compound states. In the resulting adiabatic model7), the various shapes and orientations are simply weighted by their probabilities e~FIT. Shape fluctuations in general cause a smearing of the energy distribution and an enhancement of the angular distribution, due to the contributions from large deformations with large energy splitting. The orientation fluctuations lead to a strong attenuation of the angular distribution, which usually more than compensates for the effect of large deformations. An interesting observation is that the angular distribution tends to become more pronounced with increasing spin, probably at least partly due to the reduced importance of orientation fluctuations8).

48Ji + 62Ni 48Ti + 114Cd = 34 ' Jr =33

L—.- ;

i >

Figure 6.10: GDR angular distributions, measured for 110Sn and l62Yb at Ex = 90 and 75 MeV, respectively, at various spins. The lines depict various adiabatic model calculations: The solid line refers to the most probable shape and orientation only, while the dashed and dot-dashed ones include fluctuations. The figure is taken from ref.1).

If the fluctuations are rapid due to the damping, the vibrational frequency does not have time to adjust to the present shape before a leap to a new point in deformation / orientation space takes place. This situation is more complex, and dynamical effects must be taken into account910). Deforma- tions and orientations occurring rarely (having large F), are under-weighted during the averaging, and will have only a minor effect on the observables.

42 The net outcome is a reduction of the width of the Lorentzians and an enhancement of the angular distribution relative to the adiabatic model. This situation is often referred to as motional narrowing. Another new topic is the reaction dependence of the GDR characteristics: It turns out that in systems with large projectile-target asymmetry, as in the reaction O + Sm — Yb, the energy differential method yields a large first-generation GDR component, while the primary 7-ray yield measured after reactions closer to mass symmetry, e.g. Ti + Cd — Yb, is much smaller11). Several explanations have been proposed, all built upon the following assumption: In the asymmetric system, the projectile is quickly absorbed by the target, and thermodynamic equilibrium is rapidly attained. In the symmetric system, the thermalization process is much slower, find a molecule-like intermediate system may exist for a long time. The most likely explanation is that much of the available excitation energy is bound up in the deformation during this pre-thermalization stage, giving a lower effective temperature and a lower GDR emission probability12). The analysis of data from several experiments performed with the HECTOR / HELENA setup at NBI and the search for physical interpretations of observed effects are in progress.

References:

1. J. J. Gaardhøje, Ann. Rev. Nucl. Part. Sci. 42 (1992) 483

2. K. Snover, Ann. Rev. Nucl. Part. Sci. 36 (1986) 545

3. A. Holm, Unpublished internal report NBI

4. J. J. Gaardhøje et al., Phys. Lett. B139 (1984) 273

5. F. Piihlhofer, Nucl. Phys. A260 (1977) 276

6. J. J. Gaardhøje et al., Nucl. Phys. A482 (1988) 121

7. Y. Alhassid et al., Phys. Rev. Lett. 61 (1988) 1926

8. F. Camera et al., Phys. Lett. B293 (1992) 18

9. B. Lauritzen et al., Phys. Lett. B207 (1988 ) 238

10. Y. Alhassid et al., Phys. Rev. Lett. 63 (1989) 2452

11. Z. Zelazny et al., to be published

12. M. Thoennessen et al., to be published

43 Beam energy (MeV/A) Ex (MeV) I max (ft)

6.8 105 93 10.5 230 146 15.0 385 151

Table 6.2: Approximate excitation energies and maximum spins of the compound nucleus 272X for the various beam energies.

6.2.10 Pre-Fission 7-Decay in Superheavy Nuclei

J. J. Gaardhøje, J. Bacelar, A. Bracco, F. Camera, B. Herskind, W. Korten, W. Krolas, A. Maj, A. Menthe, B. Million, H. Nifenecker, M. Pignanelli, J. A. Pinston, H. v. d. Ploeg, T. Ramsøy, F. Schussler, G. Sletten, T. S. Tveter and Z. Zelazny Measurements of neutron multiplicities from hot fissile nuclei at various initial excitation energies reveal that the number of pre-fission neutrons emitted increases with 2?*, while the number of post-fission neutrons stays approximately constant1). This result suggests that fission is a slew process, taking place only when the nucleus has been cooled to an excitation energy of Ex < 100 MeV, contrary to statistical expectations. Since neutron evaporation is obviously able to compete favourably with fission at high temperatures, this should also be the case for GDR 7-ray emission. Recent experiments measuring 7-rays from fissioning systems confirm this idea: Both a pre-fission and a post-fission component can be discerned in the 7-spectra, at different 7-energies due to the different radii of the compound nucleus and the fragments2).

The pre-fission GDR radiation offers insight into nuclear behaviour at extreme conditions with respect to spin and nucleon number, a region which has previously been closed to direct scrutiny. At spins far above the fission limit, the nucleus is expected to develop exotic shapes on its way towards scission, which will be reflected in the energy splitting and the angular distribution. The yield of pre-fission GDR 7-rays contains information about the time constant for the fission process, which is related to the viscosity of nuclear matter. At the SARA Cyclotron Laboratory in Grenoble, the superheavy nucleus 2J|X has been synthesized employing the reaction 40Ar + 232Th —* 273X. A pilot experiment was carried through by the HECTOR collaboration in 1989, using beam energies of 6.8 and 10.5 MeV/A 3). The main experiment was made in 1991, with beam energies of 10.5 and 15.0 MeV/A. Rough estimates of the corresponding excitation energies and maximum spins are given in table 6.2.

The experimental setup included the 8 BaF2 HECTOR detectors, now mounted

44 in the plane perpendicular to the beam axis. An array of small BaF2 crystals defined the events in time and served as a common start for time-of-flight measurements. Four PPACs (Parallel Plate Avalanche Counters) were used for detection of the fission fragments, one pair of plates with a sensitive area of (15.8 x 17.8 cm) p'aced above and below the beam axis immediately downstream from the target, another (24.0 x 35.0 cm) pair located to the left and the right of the beam. The position sensitivity was obtained by means of two parallel layers of wires carrying high-voltage, one wire set parallel, the other perpendicular to the beam direction. The trajectory of a fragment is uniquely defined by its intersection point (z,y) with the PPAC.

Figure 6.11: The experimental setup used in the 1991 Grenoble experiment, including the 8 HECTOR detectors and the 4 PPACs.

The parameters recorded in each event were the E, of each high-energy 7-ray absorbed in HECTOR, and the corresponding time-of-flight. In addition, the PPACs provided the (x,y) coordinates of the fission fragments, their times-of-flight and the energy loss in the detector. In this case, the angular distribution is measured relative to the spin vector, which is perpendicular both to the beam axis and the fission axis, the line connecting the two fission fragments in the center-of-mass system. For so- called binary events, where both fission fragments are detected in a pair of

45 opposite PPACs, the direction of the spin vector is readily determined. The angular distribution is found by fixing the 7-detector and measuring the 7-ray yield in coincidence with fragments with their fission axis at various angles. For this geometry, gain matching and stabilization is much less crucial. With the spin axis known, only the azimuthal averaging in the intrinsic coordinate system due to collective rotation must be taken into account. The anisotropy observed will have opposite sign and be twice as large as the one measured relative to the beam axis. Due to the disappearance of shell effects at high temperature, hot thermalized fissile nuclei tend to decompose into two fragments of approximately the same mass. Assuming that the mass loss due to particle evaporation is small, the masses of the fragments in binary events can easily be calculated by means of the position and time-of-flight information together with simple kinematic relations. By gating at symmetric fission of very heavy systems formed using heavy projectiles, we can select events preceded by complete fusion reactions and full thennalization4). Our plans are to compare the 7-spectra extracted in coincidence with symmetric fission, with theoretical calculations performed with a modified version of the program CASCADE5). The new program, implemented by M. Thoennessen and R. Butsch, compute the total statistical decay of both the compound nucleus and the fission fragments6). Traditional statistical expressions are used for particle and 7-emission rates. Fission is assumed to be a time-consuming process since it involves the relative motion of large interpenetrating pieces of nuclear matter, and may be slowed down by internal friction. The time dependence of the fission rate is described by the expression r,(i) = rfw((l + 72)1/2 - 7)(1 - e-1"'™) (6.12) where 7 is the nuclear friction coefficient and 77(7) is the average time needed to build up the stable diftusional motion towards the saddle point. is the Bohr-Wheeler fission rate expected on basis of purely statistical considerations. It is proportional to the probability for the nucleus to attain a deformation corresponding to the saddle point (at which fission is inevitable), which again is proportional to the saddle point level density at the excitation energy and spin of interest. Previous calculations made for the reaction l60 + 208Pb — 224Th suggest a friction coefficient 7 of the order of 5 - 10 6). Assuming that the excitation energy at which fission takes place is essen- 7 tially independent of the initial Ex, the energy differential method ) can be employed to obtain information about the earliest decay steps. We will attempt to isolate the energy distribution and the angular anisotropy of the pre-fission GDR radiation by means of the difference spectrum of the 15.0 and 10.5 MeV/A runs. If the ongoing data analysis is successful, we will for the first time be able to obtain detailed knowledge about the structure of a superheavy nucleus (.A = 272) at an excitation energy of « 250 - 350 MeV and a spin up to 150 ft.

46 40Ar + 232Jh = 272(l 08) 10*

2 103

2 £102

2 1C1

2 10°

Figure 6.12: Gamma-ray spectra measured for the reaction 40Ar + 332Th at 6.8 (left) and 10.5 (right) MeV/A. The lines represent various statistical model calculations. The figure has been taken from ref.8).

References:

1. D. J. Hindr; et al., Nucl. Phys. A502 (1989) 497 2. M. Thoennessen et al., Phys. Rev. Lett. 59 (1987) 2860 3. J. J. Gaardhøje et al., Nucl. Phys. A520 (1990) 575 4. B. Back et al, Phys. Rev. C32 (1985) 195 5. F. Puhlhofer, Nucl. Phys. A260 (1977) 276 6. R. Butsch et al., Phys. Rev. C44 (1991) 1515 and references therein 7. J. J. Gaardhøje et al., Phys. Lett. B139 (1984) 273 8. J. J. Gaardhøje, Ann. Rev. Nucl. Part. Sci. 42 (1992) 483

47 6.3 Rotational and High-Spin Nuclear Physics

6.3.1 Interpretation of Bands in 183Er within the Tilted Ro- tation Scheme

A. Brockstedt, J. Lyttkens-Lindén, M. Bergstrom, L.P. Ekstrom, H. Ryde, J.C. Bacelar, S. Frauendorf, J.D. Garrett, G.B. Hagemann, B. Herskind, F.R. May and P.O. Tjørn Rotational bands built on complex high-K states provide a specific possibility to study the competition between extreme angular momentum coupling schemes. Excited bands above the yrast line can be successfully described as quasiparticle configurations in a deformed potential rotating uniformly about one of its principal axes, usually referred to as principal axis cranking (PAC). An arbitrary direction of the rotational axis may, however, become a very definite possibility for certain specific configurations. The reason is that the collective angular momentum needed to describe the higher members of the band must point in another direction than the spin of the band head, which is described by non-collective cranking about the principal axes i and 3, respectively. If axial symmetry is a reasonable assumption fo." the configurations of interest one deals with two-dimensional cranking (2D), i.e. the axis of rotation and two of the principal axes, say 1 and 3, are in one plane, referred to as tilted axis cranking (TAC). A special feature for a TAC solution is that parity but not signature is a good quantum number. Ac- cordingly, it is interpreted as a rotational band of definite parity composed of all possible I-values (A I = 1 bands).

The experiment presented here was performed in order to study the structure of low-lying, high-K states in the odd-N nucleus 163Er. High spin levels ?je readied in 150Nd(18O,5ri) reactions at a beam energy of 83 MeV, supplied by the NBI Tandem Accelerator. The experiments are performed using the multi-detector system NORDBALL. Several high-K states have been observed with rotational bands built on two of them. A characteristic feature of these high-K bands is the lack of signature splitting and the presence of AI = 1, Ml transitions, which due to the high K-value compete successfully with the collective E2 transitions. The four new rotational sequences observed in the present experiments (Kl and K2 in fig. 6.13) are interpreted as configurations involving a 7~ r-state coupled to the i/[642]5/2+ or the i/[523]5/2~ state, respectively, an interpretation also consistent with the measured B(M1)/B(E2) ratios.

From our model calculation for 163Er the lowest two-quasiproton excitation in the Z=68 subsystem has one quasiparticle in the 7/2" orbital (from the 7rhn/2 subshell) and the other one in the 7/2+ orbital (from irg7/3). This particular state [7/2~ w 7/2+]„ exhibits a rather steep independence driving towards tf=0°. The calculation shows that the total projection of the angular momentum onto the 3-axis is nearly 7 ft thr oughout the whole tf-range. This 7" state is a combination of a Fermi aligned (FAL) /iu/2 and a deformation aligned (DAL) normal parity state.

48 Figure 6.13: Experimental Routhians (left) and calculated total Routhians at hw = 0.15 (mid) and 0.3 MeV (right). The inset demonstrates the tilting angle as a function of frequency for the configuration Kl.

In order to construct the near-yrast spectrum of 163Er we have combined the 7~ state (see above) with an odd neutron in the [624]5/2+, or the [523]5/2~ state. A PAC calculation (t?=90°) predicts the first ft13/2 quasicrossing at hu=0.21 MeV. The figure shows the resulting total TAC routhians at rotational frequencies ftu>=0.15 and 0.3 MeV. Their minima can be directly compared with the relative positions of the experimented routhians. The curves 1 and 1', representing the ftn/j bands (A and B), are PAC solutions, i.e. d=90°. As is also seen in fig 6.13 all other solutions are of TAC type, i.e. i? < 90°, i.e. we assign to each configuration a complete A I =1 sequence. The low-lying negative parity band (curve T) is situated in-between the two ci'u/a signature branches, which is also seen in the experimental pattern though at a slightly higher frequency. At fiu>=0.15 MeV the tilting angle is substantial (654). This agrees with the experimental observation that there is no signature splitting in the band. For 0.30 MeV the tilting angle is 85°, approaching the PAC solutions, and the onset of a signature splitting in the experimental energies is seen. For the [505]ll/2~ band (curve 3) for ftui=0.15 MeV, the solution at «9=0° represents the non-rotating intrinsic state. At tuu=0.30 MeV there is a solution at t?=70°, in agreement with the observation that the [505] 11/2" band starts between the two frequencies. The configuration {x[523]7/2_:-:Tr[404]7/2+c

49 frequency. This is in accordance with the experiment, where K2 starts at hu ~ 0.17 MeV.

6.3.2 Delayed Crossing in the Unfavoured Signature Partner 163 of the h9/2[54l]l/2- Band in Tm

H.J. Jensen, G.B. Hagemann, P.O. Tjørn, A. Atac, M. Bergstrorn, A. Bracco, A. Brockstedt, H. Carlsson, P. Ekstrom, J.M. Espino, B. Herskind, F. Ingebretsen, J. Jongman, S. Leoni, R.M. Lieder, T. Lonnroth, A. Maj, B. Million, A. Nordlund, J. Nyberg, M. Piiparinen, H. Ryde, M. Suga war a and A. Virtanen

The strongly shape driving irh9/2[54l]l/2~ configuration with a = +1/2 exhibits some anomalous, and so far unexplained, features concerning the crossing frequency, hu>c, the aligned angular momentum, ix, and interaction strength, at the alignment of the first pair of t13/2 quasineutrons in several odd Z-rare earth-nuclei. Similar information on the unfavoured a = —1/2 signature partner of the h9/2[54l]l/2~ configuration has usually not been established in high spin spectroscopy, since this band is very weakly populated

ft CO (MeV) fici) (MeV) Figure 6.14: Experimental alignment of the two signatures of the [54l]l/2~ band (open and filled circles) and the [41l]l/2+ band (open and filled squares) in 163Tm and 167Tm sis a function of rotational frequency, hu rel- 3 1 ative to the same reference with Harris parameters 30 = 40ft MeV" and Si = 40ft4MeV~3.

The nucleus 163Tm was populated in the (37C1, xn) reaction. The 7-rays were detected using the NORDBALL array equipped with 20 Compton suppressed Ge-spectrometers, and an inner BaF2 ball used to select the 4n reaction channel. A total of more than 2 • 10° two and higher fold coincidence events were collected. The results from this data concerning the

50 h9/2[541]l/2-, a = +1/2 and h,i/a[523]7/2-, a = ±1/2 configurations are given in ref.1). A more detailed analysis of the data using a clean "cube" of ~ 1.3 • 10s triple fold events selected from the 4n channel has revealed a new, weakly populated band, which from its decay to both the known + h9/2[541]l/2", a = +1/2 band as well as the [411]l/2 , a = +1/2 band is interpreted as the unfavoured [54l]l/2~ band. The shifts in frequency of the AB crossing is at least as large (i.e. >80keV) _ for the unfavoured signature of the 7r/i9/J[541]l/2 band as for the favoured signature partner. This new observation therefore rules out the possibility of a smaller crossing frequency shift when averaged over both signatures. The unfavoured [541]l/2~ band shows a gradual increase in alignment which causes the unfavoured signature partner to have a larger alignment than the favoured signature partner above hu> ~ 0.25 MeV in contrast to an expected difference in alignment of ~ 1ft between the two signatures. A possible explanation could be mixing of especially the unfavoured [541]l/2~ to a gamma vibration built on [541]l/2~ with K = |l/2-2| = 3/2. This gamma band has possibly been observed2) in 167Tm. Mixing between such bands can be large since they have AK — 1, and, furthermore, the unfavoured signature will mix much stronger due to the smaller energy difference.

References:

1. H.J. Jensen et al. Z. Phys. A340 (1991) 351. 2. S. Olbrich, V. Ionescu, J. Kern, C. Nordmann and W. Reichardt, Nucl. Phys. A342 (1980) 133.

6.3.3 Spectroscopy in the Odd-Odd Nucleus 16STm

J.M. Espino, C. Martinez-Torre, H.J. Jensen, G.B. Hagemann, P.O. Tjøm, A. Atac, M. Bergs trom, A. Bracco, A. Brockstedt, H. Carlsson, P. Ekstrom, B. Herskind, F. Ingebretsen, J. Jongman, S. Leoni, R.M. Lieder, T. Lonnroth, A. Maj, B. Million, A. Nordlund, J. Nyberg, M. Piiparinen, H. Ryde, M. Sugawara and A. Virtanen In the experiment described in the preceding contribution the nucleus 162Tm was populated in the (37C1, 5n) reaction. With this channel selected by means of the sum and fold information from the inner BaF2 ball a matrix of 7-7 coincidence events in 162Tm is being analysed. The 5 known1) bands have been extended to higher spin and 8 new bands have been established. Of these 13 bands there are 5 pairs of strongly coupled signature partners with pronounced AI=1 transitions between the partners competing with the AI=2 rotational E2 decay. The lowest 2 pairs of coupled bands have 1 + been interpreted as ir [523]7/2~ ^vi13/2 (A) and ?r[404]7/2 00 vi13/2 (A). A new strongly coupled band established rather high in spin (J ~ 39) involves most likely a v [523]7/2~ coupled to the lowest negative parity neutron state, i/[52l]3/2~, as well as a pair (AB) of t13/2 aligned neutrons. The analysis is in progress.

51 References:

1. S. Drissi, J.-Cl. Dousse, V. Ionescu, J. Kern, J.-A. Pinston and D. Barneoud, Nucl. Phys. A466 (1987) 385

6.3.4 Angular Correlations in NORDBALL

A. Nordlund, M. Bergstrom, A. Brockstedt, H. Carlsson, P. Ekstrom, H. Ryde A. Atac, G.B. Hagemann, B. Herskind, H.J. Jensen, J. Jongman, S. Leoni, A. Maj, J. Nyberg and P.O. Tjøm. A method for analyzing angular correlations in NORDBALL, or any other detector array, has been developed in Lund and tested for the first time on real data. The experiment was performed at the NORDBALL-facility for two weeks in march 1990, using the reaction 160+15JSm-^1G4Yb+4n at 83 MeV beam energy. 700 million 7-7 events were produced. The NORDBALL detector system has a very high degree of symmetry and is very well suited for angular correlations. The Ge-detectors of NORD- BALL are situated in four rings with 5 detectors in each. The total number of combinations using 20 detectors is 190, however, due to the symmetry in the NORDBAT L configuration there are only nine different angular combinations pre? at. The analysis of the angular correlations by means of \2 analysis (see ref.1) for further description of the method) shows a significant M2 component in interband El transitions. The M2 mixing ratios of the different bands differ, but are within the same: band fairly constant. This could suggest the rotational sequences to be less collective than assumed before. Spectroscopic analysis has also revealed eight new rotational bands compared to earlier studies2). The well known structure of the nucleus makes ;t possible to test the cranking model in a more extensive way than has been done before.

References:

1. L. P. Ekstrom and A. Nordlund, Nucl. Instr. and Meth. A313 (1992) 421 2. S. Jonsson et al., Nucl. Phys. A449 (1986) 537

52 6.3.5 Looking for M2 Admixtures in Sideband De-Excitations

A. Nordlund, R. Bark, H. Carlsson, P. Ekstrom, S. Freeman, G.B. Hage- mann, B. Herskind, T. Lonnroth, H. Ryde, H. Schnack-Petersen, P.O. Tjørn, T. Tveter and J. Wrzesinski The rotational structure of the nucleus 1G0Er has been studied by analyzing the reaction 34S+130Te—160Er+4n at 155 MeV beam energy. The experiment was run for two weeks at the NORDBALL-facility in Nov. 1992. The main purpose of the experiment is to analyze the interband El transitions in 160Er decaying into the ground band, by using angular correlations in NORDBALL1) to look for similar M2 admixtures as those found in 1G4Yb. As 1C0Er is an even-even nucleus the rotational structure will include com- paratively few, but intense gamma transitions. This will result in well separated peaks in a 7-7 matrix, which will improve the reliability of the angular correlations. Approximately 1.2 billion events were produced, which should be enough to perform angular correlation analysis with high accuracy. The high statistics will also make it possible to examine the nuclear structure extensively using traditional spectroscopy methods. As in the earlier 164Yb experiment this will hopefully result in many new rotational bands in an effort to perform "complete spectroscopy". Such an extensive probing of the nuclear structure enables us to compare with models such as the cranking model further away from the yrast cascade.

References:

1. L.P. Ekstrom and A. Nordlund, Nucl. Instr. and Meth. A313 (1992) 421

6.3.6 High-Spin Study of 165Lu

H. Schnack-Petersen, R.A. Bark, P. Bosetti, A. Brockstedt, H. Carlsson, L.P. Ekstrom, G.B. Hagemann, B. Herskind, F. Ingebretsen, S. Leoni, N. Nica, A. Nordlund, H. Ryde and P.O. Tjørn. During March a high-spin experiment on 7?5Lu was performed at the Nord- ball facility at NBI-Risø, using the reaction: 31P+138Ba — 4n-i-t65Lu, with a beam-energy of 155 MeV, and a goldbacked target of thickness ~ 300/ig/cm2. Approximately 160 million 7-7 coincidences were collected,and sorted into a 7-7 matrix. Efficiency coefficients (representing the efficiency-variation of the Ge-detectors for different energies), and background-subtraction according to a modified Waddington-method (using background of the total projection, taking also into account the E2-bump problem,as discussed by D.C. Radford) were performed in the analysis, using the Escrlator-92 software-package of D.C. Radford.

53 The main aim of the experiment was, in addition to extend the known level-scheme, to look for the existence of a rotational band belonging to a strongly deformation-driving configuration. This point was triggered by the 163 discovery of a strongly deformed rotational band with /32 = 0.42 in Lu, which was assigned as the [660]l/2+ -quasiproton configuration2). From the analysis of the present data, additional levels have been found in the [514]9/2"-band up to spin 71/2, and in the [404]7/2+-band up to spin 55/2, the latter including a backbend (the details are still under investigation). Furthermore we have found a strongly coupled band earlier discovered by Honkanen et al.3) in an experiment on 163Lu. Since we do not see the yrast-cascade of 163Lu, it is believed to be the yrast cascade in 164Lu, which has not been investigated yet. Searching for new bands we have found a cascade, having almost identical energy transitions as the recently discovered [660]l/2+ band in 1G3Lu1), and since the yrast-cascade of 163Lu is not present in our data, we have assigned this band to 165Lu. Although the bands in the two different nuclei are almost identical for the higher spin-values, the 7-transitions differ at low spin. Thus the peaks in the spectrum of the 163Lu-band at low spin is easily distinguished, while the corresponding spectrum of the 165Lu -band is contaminated with many other sources (particularly from the [404]7/2+ -band), probably suggesting the influence of bandmixing. However more research has to be done before we can conclude anything certain in this respect. Another puzzling feature concerning this band is the alignment. By assign- ing the spin-values to the band as the corresponding values in the 163Lu-case, we can plot the aligned angular momentum versus frequency. Assuming that we can extrapolate down to u>=0, we get the alignment £0 = Ix[u> = 0) ~ Oft, in both 165Lu and 163Lu -cases. If the bands were to correspond to [660]l/2+ -structures, we would expect an alignment of i ~ 4, which is significantly different from the extrapolated value (see fig. 6.15). An alternative interpretation is that the observed band could be a mani- + festation of a [41l]l/'2 -band at high deformation (/32 = 0-42), since the [411]l/2+ configuration is not based on a high j-shell, and therefore not expected to have a large alignment like a [660]l/2+ configuration. This implies however the existence of two deformation-regimes for the same configuration.

References:

1. W. Schmitz, C.X. Yang, H. Hubel, A.P. Byrne, R. Miisseler, N. Singh, K.H. Maier, A. Huhnert and R. V*\ss, Nucl. Phys. A539 (1992) 112 2. W. Schmitz et al., Phys. Lett, (to be published)

54 tioj (MeV)

Figure 6.15: We hope in '93 to be able to clarify some of the features stressed above, especially it would be nice to find the low/medium -spin levels in the so-called [660]l/2+ -band, since this is probably the key to determine the nature of the structure of the band.

3. K. Honkanen, H.C. Griffin, D.G. Sarantites, V. Abenante, L.A. Adler, C. Baktash, Y.S. Chen, O. Dietzsch, M.L. Halbert, D.C. Hensley, N.R. Johnson, A.J. Larabee, I.Y. Lee, L.L. Riedinger, J.X. Saladin, T.M. Semkov and Y. Schutz, in ACS Symposium Series No.324, Nu- clei far the Line of Stability. ed.R.A. Meyer and D.S. Brenner, 1986, American Chemical Society, p.317

6.3.7 High Spin States in 166Hf

M. Bergstrom, A. Brockstedt, H. Carlsson, P. Ekstrom, A. Nordlund, H. Ryde, P. Bosetti, S. Leoni, A. Bracco, B. Million, F. Ingebretsen, P.O. Tjøm, A. Atag, G.B. Hagemann, B. Herskind, H.J. Jensen, J. Nyberg, T. Lonnroth, J. Jongman, R.M. Lieder, M. Sugawara, A. Virtanen, J.M. Espino High spin states in ie6Hf have been produced by the reaction mSn(48Ti,4n) at a beam energy of 215 MeV. About 160 million events were collected during the experiment. The NORDBALL detector array consisted of 19 compton suppressed Ge detectors and one planar LEP detector. An inner ball consisting of 39 BaF2 scintillator crystals was used for multiplicity and sum energy to separate the 4n and 5n channels. The data are presently being analysed.

55 6.3.8 Interpretation of the Rotational Band Structure in 171.172W. The Importance of Small Deformation Changes

J.M. Espino, J.D. Garrett, G.B. Hagemann, P.O. Tjørn, C.-H. Yu, M. Bergstrom, L. Carlén, L.P. Ekstrom, J. Lyttkens-Lindén, H. Ryde, R. Bengtsson, T. Bengtsson, R. Chapman, D. Clarke, F. Khazaie, J.C. Lisle and J.N. Mo. High spin states of 171,172W have been investigated using the reaction 146Nd (30Si,5-4n) at a bombarding energy of 160 MeV. In mW, 4 negative parity and 2(3) positive parity bands have been established. A favoured ( —, —1/2) configuration based on the (-, +1/2) configuration (E) coupled to the (+,1) configuration (AC) is suggested to be the nature of the continuation of the (-, -1/2) band above the AB crossing. This is the first observation of the EAC configuration. The positive parity decay sequences in 171W provide an interesting extreme signature dependence for the inter-band Ml transition matrix elements, which is found to be well accounted for by theoretical expectations. In 173W four negative parity bands are established besides the positive parity yrast sequence. The interpretation of the observed rotational band structures in terms of coupling of single-quasiparticles has been strongly substantiated by very detailed theoretical cranking model calculations. A detailed description of the calculations performed for 171W and 172W is included in order to clarify the difference between a diabatic and an adiabatic treatment of band crossings. The calculations show that even small deformation changes have a significant effect on the energy spectrum. Considering such deformation changes in the calculations leads to a much •cnproved agreement with the experimental data.

Submitted to Nucl. Phys. A.

177 6.3.0 Bandcrossings and the ni13/2 Band in Re

R.A. Bark, G.B. Hagemann, B. Herskind, W. Korten M. Bergstrom, A. Brockstedt, H. Carlsson, A. Nordlund, H. Ryde, P. Bosetti, S. Leoni, P.O. Tjøm and F. Ingebretsen. When the aligned angular momentum of a rotational band of a nucleus in the rare-earth region is plotted as a function of rotational frequency, a "backbend" is usually seen corresponding to the crossing of the band by another band, usually composed of rotation aligned in/2 neutrons.

For some time the 7ril3/2 bands in the odd-proton Ir-Re nuclei have been a puzzle because of their lack of clear backbends. Instead, they have shown gradual upbends. This has been explained by considering the nucleus as being much more deformed giving rise to an apparent gain in alignment1), or by proposing strong interactions with the s-band. The apparent strong interaction has been taken as evidence of residual proton-neutron interactions outside of the mean-field approach2).

56 However, the recent results of Carlsson et al.3) (see this report) have fully revealed a sharp backbond in the Ti'13/a band of 1T1Re, calling into question the above explanations for the gradual alignment and suggesting the hypothesis of a shape-change.

This prompted our search for further backbends in xi13/2 bands in the region and as a result we have studied the nucleus 177Re with the reaction 130Te(51V,4n) at 225 MeV in a 7-7 coincidence experiment. Many bands, including those based on the 7/2+ [404], 5/2+[402], 9/2-[514], l/2-[541], l/2+[660], and presumably l/2+[411] orbit als and other 3-quasiparticle structures have been identified. The results for the l/2+[660] band show that it is crossed by another band in addition to the s-band, in a situation similar to that reported by Dracoulis et al.4) in 181Ir. The analysis is still in progress.

References:

1. G.D. Dracoulis et al., Nucl. Phys. A534 (1991) 173 2. R. Wyss and A. Johnson, Proceedings of the Conference on High Spin Physics and Gamma Soft Nuclei, Pittsburgh, 1990 3. H.C. Carlsson et al., Nucl. Phys. in press 4. G.D. Dracoulis, et al., Nucl. Phys. in press

6.3.10 Octupole Deformed States in the Radium Region

G. Løvhøiden and the IS 100 collaboration Experimental and theoretical investigations have given evidence for stable octupole deformations in nuclei in a region around A=225. Important signatures for the existence of reflection-asymmetric nuclear shapes are close- lying states of equal spins and opposite parity which are connected by fast El transitions, and "anomalous" decoupling parameters for K=l/2 bands. Such evidence has been found for nuclei around mass 225 and the present collaboration are in the process of exploring the extent of this region of octupole deformation. In fig. 6.16 is presented results from a recent measurement of the decay of 323Rn produced in the ISOLDE laboratory at CERN. It gives examples of parity doublets for K quantum numbers 1/2, 3/2 and possibly 5/2. Also the decay of Fr-isotopes have been measured in the ISOLDE laboratory. Figure 6.17 shows the change in the structure of the l/2+[63l] band with increasing mass number for radium isotopes. This probably reflects a change in the decoupling parameter with decreasing octupole deformation. More information on these recent results may be found in refs.1,3).

57 References:

1. W. Kurcewicz, G. Løvhøiden, T.F. Thorsteinsen, M.J.G. Borge, D.G. Burke, M. Cronquist, H. Gabelmann, H. Gietz, P. Hill, N. Kaffrell, R.A. Nauma n, K. Nybø, G. Nyman, J. Rogowski, Nucl. Phys. A539 (1992) 451 2. M.J.G. Borge, D.G. Burke, H. Gietz,N. Kaffrell, W. Kurcewicz, G. Løvhøiden, S. Mattson, R.A. Nauman, K. Nybø, G. Nyman, T.F. Thorsteinsen, Nucl. Phys. A539( 1992)249

736 87 712- 684 85 ('/;)*

605 43 -ill- 5,'2*

5.0 50 —— (5 2*) 519 83-2-2- 3, ug afi

1 K*= 1/2 (K = 5/2"

jnoiJSSL^r ,7'2r

171 «7 330 5,7* 188 95 -^- V 1g7 02 _L!2L 5/2" 160 45-^— 3;?* l3; 50 3/j* 100 95 H8) S/2* 82 10 —15— 7/2" 99 55 "njT 3/2" 55 oo '/>" 1150 12 90 J-L- V2- 0 "TF Figure 6.16: Rotational bands in 223Fr. The parity doublets are indicated by their K quantum numbers. In addition to excitation energies and spins, also alpha-decay hindrance factors are given for the nuclear levels.

6.3.11 Helium-Induced One-Neutron Transfer to Levels in 162Dy

E. Andersen, H. Helstrup, G. Løvhøiden, T.F. Thorsteinsen, M. Guttormsen, S. Messelt, T.S. Tveter, M.A. Hofste, J.M. Schippers and S.Y. van der Werf Backbending may be seen as a crossing of the ground state band with the S-band based on a pair of il3/2 neutrons. Little information is available on

58 3/r

675

593 6 1/2-[5011] 554.7 l/2-[501|] 518.5 3/: -i 479 2 1/2"

272 2 3/2+(6311] 236 3 5/2* 247 4 l/2+[63U] 213 0 3/2+ 221 4 3/2+[631t] 185 7 (5/2" ) x igi i 1/2+ 168.9 3/2* 150.0 3/2 M9 8 1/94 120.7 l/2+ 137.6 3/2- 90 0 3/2"

•12 8 3/2* :ll 6 3/2- + l + 0 0 l/2 0'0 0 0 5/2 o.O 5/24 [0331]

! 7 "Ra " Ra "»Ra ">T|,

Figure 6.17: Comparison of levels in 220Ra with selected levels in 225'227Ra and in the isotone 23,Th.

59 the S-band members below the crossing point. In this study1,2) such states are located in ,62Dy by means of the (a,3He) reaction on a 161Dy, which has ^ *i3/2 ground state configuration. I I I 1 . I I I !..

• 1'ITI I "10.1 . "' - h—I7J'I I fl I. VI I IM): IJ • i :> • | |7"» S lM.,,1

* 'Ul

II ci il || I>> '«'IK Figure 6.18: Ground state and S-band member in 160<163Dy with spins and excitation energies listed. For the S-band members Q-value corrected population strengths relative to the summed strength of the 4, 6 and 8 spin members of the ground state band are given.

The experiment was performed at the KVI Groningen cyclotron with a 50 MeV ct-beam. The reaction products were analysed in a QMG/2 spectro- graph and recorded in a detector that separates the outcoming a and 3He particles. As a result of this work three levels at 1578,1759 and 1990 with spin values 4, 6 and 8 have been assigned to the S-band (see fig. 6.18). The similarity both in excitation energy and population strengths for the proposed S-band members in 160Dy (ref.3)) and the present 162Dy data strongly suggests that these states are of similar nature.

References:

1. E. Andersen et al., Nucl. Phys. A273(1992)235 2. E. Andersen et al., Dept. of Phys. Report, UiO PHYS 92-34

60 6.4 High and Intermediate Energy Nuclear Physics

6.4.1 Isotopic Effects in Light Fragment Emission

M. Guttormsen, G. Løvhøiden and the CHIC collaboration

Detailed information about the emission of complex fragments in intermediate energy heavy ion reactions is important in order to understand how fast and homogeneously an excitation energy up to hundreds of MeV can be dis- tributed in nuclei. The key question for reactions in the energy 20A - 40 A MeV is wether evaporation from one incompletely fused compound nucleus dominates the emission of light and medium heavy fragments or if a fast fragmentation process followed by secondary decay contributes significantly. The experiment was performed at Gustaf Werner Cyclotron in Uppsala using a 32 A MeV 14N beam with an average current of 10 nA. Self-supporting enriched targets "? 112,124Sn with thicknesses around 1 mg/cm2 were used. Fragments were observed at 60° by two Si telescopes each consisting of five transmission detectors with thickness ranging from 14 /un to 3500 fan. Inclusive cross sections of 1'2 3H, 3'46He, 6'7'8'9Li and 7'91011Be fragments have been measured. Apparent temperatures of 4.9 MeV for an incomplete fusion source and 10- 14 MeV, from the slope of the energy spectra are found. More details on this work is found in ref.1).

References:

1. V. Avdeichikov et al., submitted to Phys. Lett.

6.4.2 Measurements of K+-Mesons at SIS

M. Guttormsen, G. Løvhøiden and the CHIC collaboration

At GSI (Darmstadt) the CHIC collaboration has installed an experimental set-up at the target used by the KAOS-spectrometer group with the purpose of measuring low energy positive kaons as a complement to the spectrometer measurements. The range telescopes consist of a stack of plastic scintillators surrounded by muon detectors. The system should be able to measure K+ in the kinetic energy range from 15 to 130 MeV in 8 consecutive bins. The identification of the K+ is possible by the muon from the process K+ - /i* + v , (6.13) with a branch of 63.5 % and a lifetime for the muon of r(v) = 12 ns. Analyses of the data is in progress.

61 6.4.3 Strangeness Production in Ultrarelativistic Nucleus- Nucleus and Proton-Nucleus Collisions

G. Løvhøiden and the NA36, WA94, WA97 Collaborations In the past few years there has been a lot of interest in the search for the quark gluon plasma . One of the possible signals for the plasma is an enhanced production of strange particles. The measurement of strange particle production in heavy ion collisions is the main objective of the NA36, WA94 and WA97 CERN collaborations. Traditionally, nuclear physicists have studied nuclear matter in its ground state condition at temperatures near zero and nuclear density close to nor- -3 mal density of nuclear matter at p0 = 0.17 Cm . Only in recent years it has become possible to deposit enough energy in the nucleus to study the properties of strongly excited nuclear matter. Reaching excitation energies of tens of GeV per nucleon, the density of hadrons is so high that the traditional picture of distinct hadrons breaks down. These densities require the hadrons to overlap, which is possible with a subnuclear structure of the hadrons. In the quark picture the hadron constituents interpenetrate the boundaries of the other hadrons, leaving the quarks free to propagate through the compressed system. The existence of such a phase transition from quark confined hadronic matter to a dense system of free quarks and gluons has been predicted by theoretical calculations1). Such a system is called a quark gluon plasma (QGP). Quark gluon plasma is a high-temperature high-density phase of strongly interacting matter. At low temperatures and densities quarks, gluons and colour fields are confined to the interior of strongly interacting hadrons. At high temperatures and densities the hadrons overlap and loose their identity; quarks, gluons and colour fields are no longer confined within hadrons but can move over distances larger than the hadron size of 1 fm. The discovery and understanding of such a phase is of fundamental importance for the theory of strong interactions. It would also serve to test the validity of concepts related to the structured vacuum of strongly interacting gauge fields. Motivated by such ideas, a new field of physics involving both nuclear and particle physicists has emerged, with a number of experimental facilities in operation which can accelerate light and medium weight nuclei to energies well into the relativistic domain. When chiral symmetry is restored, the quark mass becomes negligible, and the threshold for producing strange hadrons and baryon-antibaryon pairs is reduced. The enhanced production of strangeness as a signature of QGP was proposed by Rafelski3). In the NA36 and WA94 experiments the strange particles K°, A and A were detected with a combination of tracking devices in strong magnetic fields. In the NA36 experiment a time projection chamber (TPC) was placed in a magnetic field of 2.7 T, while WA94 used wire chambers and silicon

62 nn mass [GeV]

Figure 6.19: Invariant mass distributions for A, A and K°. The mass reso- lutions su-e 6, 6 and 7 MeV, respectively.

63 microstrip detectors in the CERN OMEGA magnet with a field of 1.8 T.

m± [GeV] Figure 6.20: Transverse mass distributions for A, A and K°.

As an example of the quality of the experimental data, the invariant mass distributions for A, A and K° are shown in fig. 6.19. These data are from the NA36 S+Pb experiment with a projectile energy of 200GeV per nucleon. The source temperatures deduced from the transverse mass spectra are given in fig. 6.20. In the NA36 experiment also p+Pb reference data were taken. In fig. 6.21 is given a comparison of S+Pb and p+Pb rapidity distributions for A, A and K° particles. It is interesting to notice that distributions found in the ion collision are all peaked close to mid-rapidity, while those observed for p+Pb tend to have maxima closer to target rapidity. This feature indicates different production mechanisms in proton-nucleus and nucleus-nucleus collisions, and have been discussed by Rafelski et al.3). The data from the NA36 and WA94 experiments are still being analysed. More information may be found in ref.4).

64 References:

1. J. Collins and M. Perry, Phys. Rev. Lett. 34 (1975) 1353 2. J. R&felski and B. Miiller, Phys. Rev. Lett. 48 (1982) 1066 3. J. Rafelski et al., Phys. Lett. B294 (1992) 131 4. Abatzis et al., Phys. Lett. B244 (1990) 130 S. Abatzis et al., Phys. Lett. B270 (1991) 123 E. Andersen et al., Phys. Rev. C46 (1992) 727 E. Andersen et al., Phys. Lett. B294 (1992) 127 E. Andersen et al., Nucl. Phys. A544 (1992) 309c

,.. .. i . i •. i TjTTTTjrrr 0.06 • S+Pb o p+Pb 4 A 0.04 3

2\~- 0.02

o o o l"ii| 111111111; 1111 $ £ + + 0.008 C0 0.006 i 5 dT $ 0.004 o*

c 0 B •a § ! ° ° § } 11111 Fi 11! 1111111 M j 11111111 i C 3 (0

1.5 2.0 2.5 3.0 3.5 Rapidity

Figure 6.21: Rapidity distributions for A, A and K° for S+Pb and reactions.

65 Chapter 7

Theoretical Nuclear Physics

The aim of our work in nuclear theory is to understand the many features of nuclear structure revealed in nuclear reactions. Most of our efforts are devoted to the calculation of nuclear properties from first principles. This involves calculating the shell-model effective interaction, starting from the free nucleon-nucleon interaction and using many-body perturbation methods. We have calculated effective interactions for a large variety of nuclear systems. Most recently, we have constructed an effective interaction for the neutron-deficient Sn-isotopes, starting from modern meson-exchange nucleon-nucleon potentials. To calculate the structure of such nuclei requires large scale siiell-model cal :ulations based on the Lanczos algorithm. To our knowledge, this is the first realistic shell-model calculation ever performed for this mass region.

A popular testing ground for the nuclear many-body problem is represented by infinite nuclear matter. Here, we have studied alternative methods for defining the single-particle potential in nuclear matter. This has been extended to neutron matter, where we have derived a new equation of state which will be applied to calculation of the basic properties of neutron stars. With members of the Bergen group we are studying the collective properties of nuclear matter as they appear in relativistic heavy-ion collisions. In particular, we have studied the thermal properties of excited dilute nuclear matter with a momentum-dependent effective interaction. The possibility of obtaining a phase transition from hadronic matter to quark-gluon plasma is examined in some detail. Further applications of nuclear many-body theory include studies of subnu- cleonic degrees of freedom. An example is evaluation of the contribution from the isobar degrees of freedom to the imaginary part of the optical- model potential for finite nuclei. Also, the modification of the isoscalar axial current of the nucleon due to the nuclear medium has been studied. We do also study problems related to the foundations of quantum physics such as the non-separability of systems in a pure quantum state and the completeness of quantum mechanics. Further studies will be made of some of the main interpretations of the quantum theory and of alternative theo-

66 ries. An analysis will be attempted on the basis of Bohr's complementarity concept and his understanding of the nature of measurements involving ac- tions of the order of the Planck constant.

7.1 The Nuclear Many-Body Problem and Nu- clear Structure

7.1.1 Studies of the Effective Interaction for Finite Nuclei

T. Engeland, M. Hjorth-Jensen, A. Holt and E. Osnes In a series of papers1-7) we have investigated the nuclear many-body problem from a perturbative point of view, i.e. through the effective interaction approach. Several nuclear systems have been studied, ranging from mass number A = 4 till A = 108. The perturbative many-body formalism we employ to derive an effective interaction has been exposed in refs.1'2). As an example of the power of our many-body approach we focus here on recent work by us on the structure of neutron deficient Sn isotopes6). For other mass areas, such as A = 40 or A = 16, the reader is referred to the references1-7) below. For a more general survey, see e.g. ref.2).

References:

1. M. Hjorth-Jensen, E. Osnes and H. Miither, Ann. of Phys. 213, 102 (1992) 2. M. Hjorth-Jensen, T. Engeland, A. Holt and E. Osnes, Physics Re- ports, in press 3. M. Hjorth-Jensen, T. Engeland, A. Holt and E. Osnes, Nucl. Phys. A541, 105 (1992) 4. M. Hjorth-Jensen, E. Osnes and T.T.S. Kuo, Nucl. Phys. A540, 145 (1992) 5. E. Osnes, M. Hjorth-Jensen, T. Engeland and A. Hclt, in proceedings of "The international workshop on Nuclear Structure Models", Oak Ridge, 16-26 March 1992, USA, (World Scientific, Singapore, 1992) p. 370

6. T. Engeland, M. Hjorth-Jensen, A. Holt and E. Osnes, University of Oslo report UIO PHYS 92-41, submitted to Phys. Rev. 7. E. Osnes and D. Str ittman, Phys. Rev. C45, 662 (1992)

67 7.1.2 The Structure of Neutron Deficient Sn Isotopes

T. Engeland, M. Hjorth-Jensen, A. Holt and E. Osnes During the last years, through the radioactive nuclear beams program, a rich varif ty of data has become available for nuclei far from the stability line. Recently, substantial progress has been made in the spectroscopic approach to the neutron deficient doubly magic 100Sn core. From the in-beam analyses in refs.3-5) knowledge of the proton-proton and proton-neutron residual interaction and the single-particle energies has been obtained. However, information on the neutron-neutron interaction in this mass area is rather scanty. Furthermore, only properties of 100Sn have been studied theoretically, using either approaches inspired by the relativistic Serot-Walecka model, such as the calculations of Hirata et a/.6) or that of Nikolaus ct. al.7), or the use of non-relativistic models as done by Leander et al.8). Properties like binding energies, mean charge radius, proton and neutron single-particle energies can be obtained from the above analysis. However, no calculations of realistic neutron-neutron effective interactions have been mounted in this mass area. Here we derive a two-body neutron-neutron effective interaction calculated from conventional perturbative many-body techniques2).

Basically, the effective interaction approach can be divided into three steps: First, one needs a nucleon-nucleon interaction (NN) V which is appropriate for nuclear physics at low and intermediate energies. At present, a meson- exchange picture for the potential models seems to offer a viable approach to the NN interaction V. Among such meson-exchange models, one of the most successful is the one presented by the Bonn group9). As a starting point for our perturbative analysis, we will therefore use the parameters of the Bonn A potential as they are defined in table A.2 of ref.°). Secondly, in nuclear many-body calculations, the first problem one is con- fronted with is the fact that the repulsive core of the NN potential V is unsuitable for perturbative approaches. This problem is however overcome by introducing the reaction matrix G given by the solution of the Bethe- Goldstone equation

g = v + v1i^Qg' <71>

where (I is the energy of the interacting nucleons in a medium, and H0 is the unperturbed hamiltonian. The operator Q, commonly referred to as the Pauli operator, is a projection operator which prevents the interacting nucleons to be scattered into states occupied by other nucleons. In this work we solve eq. (7.1) for five starting energies fi, by way of the so-called double- partitioning scheme defined in ref.10). The Pauli operator is constructed so as to prevent scattering into intermediate states with a nucleon in any of the states defined by the orbitals of from the la to the lharmonic- oscillator (HO) basis was chosen for the single-particle wave functions, with an oscillator energy ftu>,u > being the oscillator frequency, determined through the relation hw - 45A~1/3 -- 25A~2/3 = 8.5 MeV, with A being the mass

68 number. 107Sn MeV

15/2+ 2 - 13/2+

ffiw

13/2+"/2+ 3 2+ + 9/2+ / === 9/;2 + lY#+5/2+ 9/2+ 3/2+ 7/2+ 9/2+ 1/2+

: 5/2+ 3/2+

7/2+ 7/2+ 5/2+ 5/2+

Third order Exp

Figure 7.1: Theoretical and experimental spectra for l07Sn.

Finally, we briefly sketch how to calculate an effective interaction appropriate for nuclei in the mass-100 region, within the framev-ork of degener- ate Rayleigh-Schrodinger perturbation theory. The many-body Schrodinger equation for an A-nucleon system is defined in terms of an equation acting within a physically appropriate subspace of the full Hilbert space (the model space), defined by a projection operator P, with P + Q — 1. This equation defines an effective hamiltonian HCfj in the actual model space. In this work we define the model space to consist of the orbitals in the sdg shell except the 1 go/2 orbital which is a hole. Moreover, as we show below, the inclusion of the l/in/2 orbit to our model space is needed in order to obtain

69 a quantitative description of the data. To calculate the effective interaction we employ a method presented by Lee and Suzuki (LS) to sum up so-called folded diagrams11), which arise due to the removal of the dependence on ;he exact energy of the Rayleigh-Schrodinger expansion. The starting point for this partial summation of a class of diagrams is to define the so-called Q-box, which is defined as the sum of all non-folded linked and irreducuble diagrams to a given order in the interaction, defined in terms of the G-matrix as Q(n) = G(n) + where H0 is the unperturbed hamiltonian. The energy ft is the unperturbed energy of the interacting nucleons. The LS expansion for the effective interaction is then formally given as

Httf = Ho + lim Rn,

with -1 Rn = l-Ql-^Qm n Q m=2 fc=n-m+l

Here we have defined Qm = with E being the energy at which one wants to evaluate the effective interaction. To define the Q-box, we include all diagrams through third order in the interaction, as defined in the appendix of ref.1). Five iterations were sufficient in <. rder to obtain a stable result. As an example of our calculations, we show in fig. 7.1 the low-lying theoretical and experimental spectra of 107Sn.

References:

1. M. Hjorth-Jensen, E. Osnes and H. Miither, Ann. of Phys. 213, 102 (1992) 2. M. Hjorth-Jensen, T. Engeland, A. Holt and E. Osnes, Physics Re- ports, in press 3. R. Schubart ct al., Z. Phys. A343, 123 (1992) 4. R. Schubart ct al., Z. Phys. A340, 109 (1991) 5. H. Grawe ct al., Prog. Part. Nucl. Phys. 28, 281 (1992) 6. D. Hirata ct al., Phys. Rev. C 44, 1467 (1991) 7. T. Nikolaus, T. Hoch and D.G. Madland, Phys. Rev. C 46, 1757 (1992) 8. G.A. Leander, J. Dudek, W. Nazarewicz, J.R. Nix and Ph. Quentin, Phys. Rev. C 30, 416 (1984)

70 9. R. Machleidt, Adv. Nucl. Phys. 19, 189 (1989) 10. E.M. Krenciglowa, C L. Kung, T.T.S. Kuo and E. Osnes, Ann. of Phys. 101, 154 (1976) 11. K. Suzuki and S.Y. Lee, Prog. Theor. Phys. 64 (1980) 2091

7.1.3 Isobar Contributions to the Imaginary Part of the Optical' Model Potential for Finite Nuclei

M. Hjorth-Jensen, H. Miither", M. Borromeo" and A. Polls'' " Institut fur Theoretische Physik, Universitåt Tubingen, Fed. Rep. Germany 6 Departament d'Estructura i Constituentes de la Materia, Universitåt de Barcelona, Spain

When a nucleon enters a nucleus, there is a sizable probability that the target will be excited and thence the incoming nucleon will be absorbed fiom the elastic channel. The effect of this absorption can be accounted for by way of an imaginary part W of the mean field describing the interaction between a nucleon and a nucleus. This mean field is actually what defines the optical-model potential. The imaginary part vanishes, or is rather small in the energy domain that corresponds to energies near the Fermi level. Certain nuclear states at these low energies can directly be identified with a single-particle configuration. However, for excitation energies large relative to the Fermi energy, one can no longer establish such a correspondence between a single-particle configuration and a given nuclear energy level. The single-particle strength is then shared among many levels. The strength function of e.g. the d5/3 hole state in 39Ca is shown to be highly fractionated in the energy region 4-10 MeV, mainly because the single-hole state couples to the collective phonon motion in the 40Ca core. The main fraction of the strength function is however located near some selected energies, to be referred to as quasiparticle energies. The energy domain in which most of the single-particle strength remains located is called the quasiparticle spreading width I\ This spreading width is related to the imaginary part of the optical potential.

The same processes which lead to an imaginary part for the self-energy (se. e.g. the diagrams displayed in fig. 7.2 also modify the real part of the nucleon-nucleus potential. This modification of the real part is related to the imaginary part by a dispersion relation, involving the imaginary part at all energies. These properties of the imaginary part of the optical-model potential, demonstrate that the optical potential, and thereby the self-energy of the nucleon, can be considered as a key point for investigations in nuclear structure. Mi- croscopic calculations of the optical potential, the nucleon self-energy and related quantities like quasiparticle strength functions, have been carried out

71 (a) (b) (c)

Figure 7.2: Diagrams arising in the evaluation of the optical-model potential. Diagram (a) is the Hartree-Fock contribution, whereas diagrams (b) and (c) are the 2plh and 3p2h contributions, respectively. The wavy line stands for the nuclear reaction matrix G. in nuclear matter. A main advantage of studies in nuclear matter originates from the fact that the single-particle wave functions for this infinite system are plane waves. For a microscopic calculation of finite nuclei one has to consider different single-particle wave functions for bound states and for the continuum, which leads to complications in the calculation. Therefore, in finite nuclei, phenomenological methods like the one exposed ad extenso in ref.1) have been much favored. Recently, however, a technique has been developed3,3) to evaluate the real part and imaginary part of the optical potential within a microscopic approach directly for finite nuclei. This method allows for a direct calculation of the optical potential w ith all kinds of mixed representations for both particle and hole states. Since the optical-model is used for nucleon energies up to a few hundred MeV, it is of interest to study the imaginary part at such energies. Further- more, as we have discussed already above, the dispersion relation between the real and imaginary component of the self-energy relates the imaginary part also at such large energies to the real part at low energies. Therefore it is of interest to study the imaginary part also at these energies. At such energies, it is also the A(3,3) isobar which is of importance. Ti 's resonance has spin and isospin 3/2 and mass 1232 MeV, which is about 300 MeV higher than that of the nucleon. The dominant role of the A isobar as compared to other resonances of the nucleon can be understood because it is the lightest pion-nucleon resonance. It is also a rather important mechanism in describing pion-nucleon scattering. Results for 160 are presented in refs.4"6). The contributions to the imaginary part are given by the two-particle-one-hole (2plh) and three-particle- two-hole (3p2h) diagrams, see fig. 7.2. The latter contributes at negative energies only and the contribution from isobar intermediate states is rather small. The 2plh diagram receives significant contributions from isobars at energies near the resonance and above the threshold for the excitation of AA states. In particular the importance of AA configurations is rather sensitive to the treatment of short-range correlations. The parameterization of

72 Imaginary Part

Figure 7.3: Strength of the Woods-Saxon parametrization. The solid line refers to contributions due to NN correlations only, while the dashed line is obtained from isobars A only. Contributions at negative energies arise from the 3p2h diagram only, while those at positive energies are due to the 2plh contributions. the self-energy in terms of local potentials is discussed. The depletion of the occupation of the single-particle orbits due to nucleon-nucleon correlations and A excitations is evaluated. From our microscopically derived optical potential it is possible to extract the parameters used to describe a Woods-Saxon potential3). As an example we show in fig. 7.3 the strength of ne Woods-Saxon parametrization for I = 0 (ref.4)). Our results are however to be viewed as a qualitative estimate of isobar contributions, since there is a large uncertainty in the values of both coupling constants and energy cutoffs used in the evaluation of N A potentials based on meson exchange (x and p mesons in our case). Furthermore, in the above analysis we set the self-energy of the isobar equal zero, whereas a more realistic analysis should account for a finite and medium dependent self-energy. The inclusion of a finite self-energy would not only shift the peaks of the isobar contributions to lower energies, but also the width of these contributions may get modified. With a constant self-energy, the total integrated strengths of the isobar contributions are conserved, though, whether a more realistic energy-dependent self-energy conserves the total strength or not is an open question. Using the parametrization of Oset and co-workers7)

73 we have investigated the role played by a finite and energy-dependent self- energy in the evaluation of the 2plh and 3p2h diagrams. The differences with and without a finite width were however negligible®).

This work has been supported by the Norwegian research council for Science and the Humanities (NAVF), the "Bundesministerium fur Forschung und Technologie" through grant (06 Tii 714) and by the Spanish research council (DGICYT) through grant (P-i89-0332).

References:

1. C. Mahaux and R. Sartor, Adv. Nucl. Phys. 20 (1991) 1 2. D. Bonatsos and H. Miither, Nucl. Phys. A496 (1989) 23 3. D. Bonatsos and H. Mxither, Nucl. Phys. A510 (1990) 55 4. M. Borromeo, D. Bonatsos, H. Miither and A. Polls, Nucl. Phys. A539 (1992) 189 5. M. Hjorth-Jensen, M. Borromeo, H. Miither and A. Polls, Nucl. Phys. A, in press 6. M. Hjorth-Jensen, M. Borromeo, H. Miither and A. Polls, two manuscripts in preparation 7. E. Oset and L.L. Salcedo, Nucl. Phys. A468 (1987) 631

7.1.4 New Equations of State for Neutron Stars

L. Engvik, M. Hjorth-Jensen, E. Osnes, B. Gang" and E. Østgaard" ° Department of Physics, AVH, University of Trondheim, N-7055 Dragvoll, Norway T*>e physics of compact objects like neutron stars offers an intriguing inter- play between nuclear processes and astrophysicalobservables. Neutron stars exhibit conditions far from those encountered on earth; typically, expected densities of a neutron star interior are of the order 103 or more than the density at neutron drip (10ug/cm3). Thus, central to calculations of neutron star properties, is the determination of an equation of state for dense matter. Th?? determines the mass range as well as the mass-radius relationship for these stars. It is also an important ingredient to the determination of the composition of dense matter and to how thick the crust of a neutron star is. The latter influences neutrino generating processes and the cooling of neutron stars. Pertinent to this study is the derivation of the equation of state (EOS), i.e. the functional dependence of pressure P on density, for dense neutron matter

74 from the underlying many-body theory, departing from a realistic nucleon- nucleon (NN) interaction. By realistic we will mean a nucleon-nucleon interaction defined within the framework of meson-exchange theory, conventionally described in terms of one-boson-exchange (OBE) models discussed above. Explicitly, we will here depart from the Bonn meson-exchange potential models as they are defined in table A.2 of ref.1). Further, the physically motivated coupling constants and energy cutoffs which determine the OBE potentials, are constrained through a fit to the available body of scattering data. The subsequent step is to obtain an effective NN interaction in the nuclear medium by solving the Bethe-Goldstone equation self-consistently. Thus, the only parameters which enter the theory, are those which define the NN potential. Such an approach is commonly referred to as the parameter free one, in order to distinguish it from methods where the mesons masses and coupling constants are adjusted to the bulk nuclear matter properties3). Until recently, most microscopic calculations of the EOS for nuclear or neutron matter have been carried out within a non-relativistic framework3), where the non-relativistic Schrodinger equation is used to describe the single- particle motion in the nuclear medium. Various degrees of sophistication are accounted for in literature1,4), ranging from first order calculations in the reaction matrix G to the inclusion of two- and three-body higher order effects. A common problem to non-relativistic nuclear matter calculations, is however the simultaneous reproduction of both the binding energy per nucleon (BE/A = -16 ± 1 MeV) and the saturation density, with fermi momentum kp = 1.35 ± 0.05/m-1. Results obtained with a variety of methods md nucleon-nucleon (NN interactions, are located along a band, denoted the "Coester band", v' ; does not meet the empirical data for nuclear matter. Albeit these deficiencies, much progress has been achieved recently in the description of the saturation properties of nuclear matter. Of special rele- vance is the replacement of the non-relativistic Schrodinger equation with the Dirac equation io describe the single-particle motion, referred to as the Dirac-Brueckner (DB) approach. This is motivated by the success of the phenomenological Dirac approach in nucleon-nucleus scattering and in the description of properties of finite nuclei5), such as e.g. the spin-orbit splitting in finite nuclei0). Moreover, rather promising results within the framework of the DB approach, have been obtained by Machleidt, Brockmaim and Miither7-3), employing the OBE models of the Bonn group. Actually, the empirical properties of nuclear matter are quantitatively reproduced by Brockmann and Machleidt7).

In this work10) we calculate the surface gravitational redshift, radius, mass and moment of inertia for neutron stars using various equations of state (EOS). The latter are derived from the recent meson-exchange potential models of the Bonn group. Here we derive both a non-relativistic and a relativistic EOS. Relativistic effects are known to be important at high densities, yielding an increased repulsion. This leads in turn to a stiffer EOS compared to the EOS derived with a non-relativistic approach. The implications for the various neutron star properties studied here are discussed.

75 References:

1. R. Machleidt, Adv. Nucl. Phys. 19 (1989) 189 2. S.D. Serot and J.D. Walecka, Adv. Nucl. Phys. 16 (1986) 1 3. R.B. Wiringa, V. Fiks and A. Fabrocini, Phys. Rev. C38 (1988) 1010

4. C.J. Pethick and D.G. Ravenhall, Phil. Trans. R. Soc. Lond. A341 (1992)17 5. L.S. Celenza and C.M. Shakin, Relativistic Nuclear /'/ly.sio: Theories of Structure and Scattering, Vol. 2 of lecture Notes in Physics, (World Scientific, Singapore, 1986): B. ter Haar and R. Malfliet, Phys. Rep. 149 (1987) 207: T. Nikolaus, T. Hoch and D.G. Madland, Phys. Rev. C46 (1992) 1757

6. R. Brockmann, Phys. Rev. C18 (1978) 1510 7. R. Brockmann and R. Machleidt, Phys. Rev. C42 (1990) 1965 8. H. Muther, R. Machleidt and R. Brockmann, Phys. Rev. C42 (1990) 1981 9. G.Q. Li, R. Machleidt and R. Brockmann, Phys. Rev. C46 (1992) 2782 10. L. Engvik, B. Gang, M. Hjorth-Jensen, 12. Osnes and E. Østgaard, in preparation

7.1.5 Model-Space Brueckner-Hartree-Fock Calculations for Nuclear Matter

L. Engvik, M. Hjorth-Jensen, E. Osnes and T.T.S. Kuo" a Department of Physics, SUNY at Stony Brook, USA In this work1) we have examined a model-space Brueckner-Hartree-Fock (MBHF) approach to the single-particle energies in nuclear matter employing three recent versions of the Bonn meson-exchange potential model. The non-relativistic MBHF calculations form the well known "Coester" band, where the potential which exhibits the weakest tensor foi ce yields the largest binding energy per nucleon. Correcting for relativistic effects, the MBHF calculations result in too little binding, however, we argue that, by introducing higher-order effects such as the summation of ring-diagrams, one meets the empirical area.

76 References:

1. L. Engvik, M. Hjorth-Jensen, E. Osnes and T.T.S. Kuo, University of Oslo report UIO PHYS 92-30

7.1.6 Nuclear Renormalization of the Isoscalar Axial Cou- pling Constants

M. Hjorth-Jensen, M Kirchbach", D.O. Riska1 and K. Tsushima1 " Institut fur Kernphysik, TH Darmstadt, Germany 6 Department of Physics, University of Helsinki, Finland c Research Institute for Theoretical Physics, University of Helsinki, Finland Experiments on deep inelastic muon1,2) and neutrino scattering on nuclei3) indicate that the axial current of the nucleon has an isoscalar component in addition to the conventional isovector component. In the case of a free nucleon the isoscalar axial current is associated with the presence of a as component in the nucleon wave function. Although the empirically obtained values for the isoscalar axial current coupling constant Gf have large uncertainty limits, both types of experiment give values for Gf that agree in sign and magnitude. Another type of experiment that should be able to yield information on Gf are measurements of the parity violating observables associated with electron-nucleus scattering4). This then raises the question as to which degree the value of Gf will be renormalized from the free nucleon value in the nuclear medium.

The analogous nuclear renormalizations of the isovector axial charge and current coupling constants form an interesting and nontrivial topic. On the one hand second order configuration mixing of the nucleon states and exchange current effects are known to cause a quenching of the axial current coupling constant, g%T, the magnitude of which is about 30%, in ad shell nuclei5). On the other hand the value of the axial charge which equals g$T for free nucleons, is strongly enhanced by up to 100% in heavy nuclei6'7) by exchange current effects8'9). The main difference between the exchange current contributions to the effective isoscalar and isovector axial charge coupling constants is the absence of any long range pion exchange current contribution to the former. A contact coupling of the isoscalar axial vectOT field to the pion would be possible only through the small w - tj - r}' mixing. In the case of bound nucleons there is nevertheless a pion exchange contribution to the isoscalar axial current that is associated with the iroo(980) exchange mechanism. This mechanism would contribute an effective isoscalar spin current for a nuclear nucleon even in the absence of any strange quark content of the nucleon. The exchange current operators that contribute to the effective single nucleon current operators fall into two classes. The first of these classes is formed of those two-body currents, the presence of which is implied by the form of the nucleon-nucleon interaction, and the second of the two-body

77 currents that involve transition couplings between non-nucleonic components and which thus involve coupling parameters that do not appear in the nucleon-nucleon interaction. Methods have recently been developed for con- structing the former type of exchange current operators - "the model independent ones" - directly from the potential model*-10,11). The only isoscalar axial exchange current of the second (model dependent) type that we shall consider here is that associated with the xoo exchange mechanism. The focus will however be on the calculation of the exchange current renormalization of the effective isoscalar axial coupling constants that is implied by the nucleon-nucleon interaction, using the method suggested in ref.8-11). The isoscalar axial exchange current operators of main importance that we consider may be represented as the non-relativistic limits of the nucleon- antinucleon pair diagrams in fig. 7.4a. As the nucleon-nucleon interaction model in these "external radiation" diagrams is assumed to be known, there is no model dependence in these two-body operators at all, except for the isoscalar axial coupling to the external nucleon line. Indirect model dependence does however arise from the fact that the nucleon-nucleon interaction is not very well known at short range. It should be emphasized that only the short range components of the rtucleon-nucleon interaction contribute to the isoscalar exchange current.

a b Figure 7.4: (a) Isoscalar axial current diagram implied by the NN interaction. (b) The Oq*(980) isoscalar exchange current diagram.

The isoscalar component of the axial current can couple to a scalar-pseudoscalar meson system. The lightest such would involve the irao(980) transition coupling. The associated contribution to the isoscalar axial exchange current operator is illustrated by the Feynman diagram in fig. 7.4b. This model dependent exchange current diagram cannot contribute to the renormalization of the axial charge at lowest order, but will lead to a renormalization of the axial current coupling. This renormalization is estimated here to amount to a quenching of about 8% of the effective axial current coupling.

In the construction of the effective single nucleon isoscalar axial current operator one sums the matrix elements of one of the two nucleon coordinates over the Fermi sea (or closed core). This procedure is sensitive to the quality

78 of the nuclear wave function model, and in particular to th* short range correlations in the two-nucleon pair wave functions. In order . o deal with this aspect properly we use a short range correlation function obt \ined from the G-matrices that correspond to the same nuclear force models which we use to construct the exchange current operator. The isosc'.lar axial current of a single nucleon may be expressed as12)

0, < P I< (0)|P >= jG?(g)fl(p')7„76«(p), where u(p) and u(p') are the initial and final nucleon spinors. The isoscalar (strangeness) form factor Gf(q) in this expression replaces the factor 2<74(4) that would appear in the conventional isovector axial current. The empirical values for the isoscalar axial coupling constant Gf (0) are 0.38 ± 0.11 (ref.1,2)) and 0.30 ± 0.16 (ref.3)). When considering the effective isoscalar axial current of the nucleon in the nuclear medium one liaj to separate the axial charge and current components. These may be denoted

—' ' 2mjv

A<°> = -^{(1 + Ss)ff+ ST[ff-pp - iff]}. Note that

This research has been supported in part by the Academy of Finland through grants 5628/5111/89 4 and 1227/3011/88 and the NORDITA.

References:

1. J. Ashman et al., Phys. Lett. B206 (1988) 364 2. J. Ashman et al., Nucl. Phys. B328 (1989) 1 3. L. Ahrens et a.' Phys. Rev. D35 (1987) 765

79 4. M.J. Musolf and T.W. Donnelly, Nucl. Phys. A546 (1992) 509 5. J. Delorme, Nucl. Phys. A374 (1981) 545c 6. E.K. Warburton, Phys. Rev. Lett. 66 (1991) 1823 7. E.K. Warburton, Phys. Rev. C44 (1991) 233 8. M. Kirchbach, D O. Riska aid K. Tsushima, Nucl. Phys. A542 (1992) 616 9. I.S. Towner, Nucl. Phys. A542 (1992) 631 10. P.G. Blunden and D.O. Riska, Nucl. Phys. A536 (1992) 697 11. K. Tsushima and D.O. Riska, Nucl. Phys. A549 (1992) 313 12. L. Wolfenstein, Phys. Rev. D19 (1979) 3450 13. M. Hjorth-Jensen, M. Kirchbach, D.O. Riska and K. Tsushima, Nucl. Phys. A, in press 14. R. Machleidt, Adv. Nucl. Phys. 19 (1989) 189 15. M. Lacombe et al., Phys. Rev. C21 (1980) 861

7.2 Nuclear Reactions

7.2.1 Momentum-Dependent Mean Field Effects on the Nu- clear Equation of State and on Phase Transition Sig- nals

E. Osnes, L.P. Csernai*, G. Fai", C. Gale*** and V. K. Mishra** " University of Bergen *' Kent State University. Ohio, USA "** McGill University, Montreal, Canada

Momentum-dependent mean fields play an important and increasing role in the description of nuclear collisions1-3). The momentum-dependence of the mean field, resulting from the fact that the nucleon-nucleon interaction is itself momentum-dependent4,5) has important implications on the static and dynamic properties of nuclear matter, e. g. the nuclear incompressibility.6,7). Most investigations of the momentum-dependence have focused to date on the intermediate energy range (Ebeam a .1 — 2GeV), but the consequences of the momentum-dependence have not been fully explored. For example, the momentum distribution of the nucleons at finite temperature will be more complicated than a Maxwell-Boltzmann distribution (in the classical limit) in the presence of a momentum-dependent mean-field. We have studied8,9) the momentum distribution in a momentum dependent mean-field and examined the consequences of the deviation from a naively

80 expected Maxwellian at medium as well as relativistic beam energies with particular attention to signals of the quark-gluon plasma transition.

References:

1. C. Gale, G.F. Bertsch and S. Das Gupta, Phys. Rev. C35 (1987) 1665 2. J. Aichelin, A. Rosenhauer, G. Peilert, H. Stocker and W. Greiner, Phys. Rev. Lett. 58 (1987) 1926 3. G.M. Welke, M. Prakash, T.T.S. Kuo, S. Das Gupta and C. Gale, Phys. Rev. C38 (1988) 2110 4. A. Bohr and B. Mottelson, Nulear Structure, Vol. 1 (Benjamin, New York, 1969) 5. W.D. Myers, privat communication (1989) 6. G.E. Brown and V. Koch, Proc. 8th High Energy Heavy Ion Study, ed. J.W. Harris and G.J. Wozniak, Berkeley, 16-?0 Nov. 1987, LBL- 24580 (1988) 29 7. G. Peilert et al., Proc. 8th High Energy Heavy Ion Study, ed. J.W. Har- ris and G.J. Wozniak, Berkeley, 16-20 Nov. 1987, LBL-24580 (1988) 43 8. L. P. Csernai, G. Fai, C. Gale and E. Osnes, Phys. Rev. C46 (1992) 736 9. V. K. Mishra, G. Fai, L. P. Csernai and E. Osnes, Phys. Rev. C ( in press)

7.3 The Foundation of Quantum Physics

7.3.1 Quantum Theory and Questions of Reality and Com- pleteness

H. Andås and K. Gjøtterud Conventionally, quantum theory is regarded as a theory giving nothing but statistical predictions for results of measurements. It therefore imparts fundamental significance both to epistemology and probability. Albert Ein- stein's misgivings about such a def .ription of natural phenomena has sur- vived him, however, and is still an incentive to continued discussions, as well as experimental verifications of questions pertaining to the interpretation of quantum mechanics. The project Quantum Theory and Questions of Reality and Completeness1) has pursued an investigation of the concepts of reality and completeness

81 of a physical theory based upon considerations made by A. Einstein, B. Podolsky and N. Rosen (EPR) in their 1935 paper2). EPR give explicit criteria for locality, reality and completeness which they expect to be obeyed by a complete description of a locally objective reality. If one defines the assignment, e.g. by a measurement, of a definite value to an observable pertaining to the physical system under investigation as an event, EPR can be interpreted as claiming that at least some such events correspond to elements of an objective reality. We have discussed the relation of the EPR criteria, transformed into probability statements, to algebras involving events and studied the consequences of such algebras in terms of the Bell-type inequalities that can be associated with probability measures definable on the algebras. Considerations of this kind are further elaborated upon in the papers Quantum Theory and Ques- tions of Reality and Completeness*) and Bell's Inequalities for Quantum Mechanics*). Also, the concept of a locally stochastic causality, pertaining to the situation in which a probability distribution for the observables associated with certain events can be regarded as stochastically connected to "hidden" elements of reality, is contemplated in the paper Bell-type Experi- ments and The. Concept of Locally Stochastic C'ausalit.jf').

It has been shown that the assumption f a Boolean algebra of events, the latter related to the notion of an "objective reality" by representing the fixations of definite outcomes to the measurements of certain observables of interest, together with a non-contextual Kolmogorov probability measure or, equivalently, a (necessarily also non-contextual) well-defined probability measure for the complete set of all (joint) events1 defining a <7-algebra6), lead to Bell-type inequalities for the expectation values of certain combinations of joint observations of pairs of observables. The non-contextuality implies the possibility of assuming factorizability of probability measures ("strong locality"3)) for independent events. The predictions of quantum mechanics, however, generally disobey Bell-type inequalities4). Nevertheless, locality in the "signalling" sense (Einstein locality) prevails also in quantum theory3,7). The incompatibility of quantum theory with a locally realistic description thus is traceable to the use of a complete description of events in terms of general Boolean or cr-algebras. Further investigations, independent of these aspects, seem to confirm this. Studies of e.g. quantum probabilities, i.e. probabilities associated with pure states, have revealed that they can only be connected to a (contextual) a- additive class of events6) and, furthermore, that the pure states cannot be accepted as complete in a way thought to be equivalent to the EPR sense of the latter3). Additionally, product states and mixtures, which do not exhibit the characteristics of a pure quantal state, according to our analysis are both local and (with the exception of general mixtures) complete in the specified sense. Moreover, they do give predictions satisfying generalized Bell-inequalities*4).

'This condition is considered to be equivalent to the existence of a joint probability distribution for the observables associable with the events.

82 It is thus concluded that the incompatibility of quantal pndictions with Bell- typc inequalities forces us to give up the notion of an independent objective nality as represented by Boulean (or sprcijicully cr-J algebras of events, or at least the hope for a complete description of such a irality as imagined by FPR2), as long as these pirdictiotis air. found to be corirct. Such notions are not based upon "direct appeals to experiments and measurements"8) bur rather on a priori philosophical attitudes and preconceptions3). The question of locality seems, however, not to be an issue since there aie no compelling reasons indicating that Einstein locality cannot be assumed. Re- linquishing independent objective reality in the sense defined above thus would involve only a "minimal" departure from the already well-established principles guiding the formation of physical theories. Furthermore, our argument is strengthened by the GHZ theorem9-11), which shows the incompatibility of quantum theory with independent reality for the deterministic case without any inequalities or locality considerations.

The considerable majority of the numerous experiments performed to test whether or not a description bused upon a locally objective reality is adequate essentially confirm that quantal predictions, and thus quantum theory in general, are correct13-20), albeit this interpretation relies also upon additional assumptions (pertaining to detector efficiencies, the non-enhancement of detection probabilities by polarizers etc.) that have to be made regarding the experimental apparatus (see e.g.21,22)). There are, however, indications that local realism cannot be saved even if the need for the assumptions made above could be eliminated23). Thus, an explicit and complete description of an objective reality cannot be expected to fully account for all the observed phenomena in nature. No definite experiiwntal rejection of a locally stochastic theory^) has yet been provided, though. However, the realisation of a GHZ-type experiment would finally settle this question for the deterministic case.

An interpretation of spin-components as "actual" versus "potential" in connection with mixtures (cfr. the discussion in section 3 of reference1)) implies the possibility of formulating a "weak" reality criterion that can be regarded as bridging the gap between local (EPR-type) reality and quantum mechanics. However, our considerations show3) that an analysis of experiments in terms of boundary conditions, i.e. the state preparation procedures, and their influence on the possibility of establishing an independent reality for the subsystems is a more interesting concept, providing more adequate tools for a further discussion, than whatever can be expected from the search for explicit reality criteria. Nevertheless, the "weak" reality criterion seems to be as close as one can get to an interesting reality concept that is found to be compatible with quantum theory.

83 References:

1. H.E. Andås, Quantum Theory and Questions of Reality and Com- pleteness, Thesis for the degree of Doctor Scientiarum, Department of Physics, University of Oslo, Oslo, December 1992 2. A. Einstein and B. Podolsky and N. Rosen, Phys. Rev. 47, 777 (1935) 3. H.E. Andås and O.K. Gjøtterud: Quantum Theory and Questions of Reality and Completeness, University of Oslo Report, UiO/PHYS/92- 24/1992. Accepted for publication in Foundations of Physics Letters 4. H.E. Andås, Phys. Lett. A167, 6 (1992) 5. H.E. Andås: Bell-type Experiments and The Concept of Locally Stochas- tic Causality, University of Oslo Report, UiO/PHYS/92-25/1992. Sub- mitted to II Nuovo Cimento B 6. S.P. Gudder, Quantum Probability (Academic Press, London, 1988) 7. G.C. Ghirardi and A. Rimini and T. Weber, Lett. Nuovo Cimento 27, 293 (1980) 8. N. Bohr, Phys. Rev. 48, 696 (1935) 9. D.M. Greenberger and M.A. Horne and A. Zeilinger in M.Kafatos (ed.), Bell's Theorem, Quantum Theory and Conceptions of The Uni- verse (Kleuwer Academic Publishers, Dordrecht, 1989) 10. D.M. Greenberger and M.A. Horne and A. Shimony and A. Zeilinger, Am. J. Phys. 58, 1131 (1990)

11. N.D. Mermin, Am. J. Phys. 58, 731 (1990) 12. S.J. Freedman and J.F. Clauser, Phys. Rev. Lett. 28, 938 (1972) 13. E.S. Fry and R.C. Thompson, Phys. Rev. Lett. 37, 465 (1976) 14. M. Lamehi-Rachti and W. Mittig, Phys. Rev. D 14, 2543 (1976) 15. A. Aspect and J. Dalibard and G. Roger, Phys. Rev. Lett. 49, 1804 (1982) 16. Z.Y. Ou arid L. Mandel, Phys. Rev. Lett. 61, 50 (1988) 17. Y.H. Shiii and C.O. Alley, Phys. Rev. Lett. 61, 2921 (1988). 18. W. Perrie and A.J. Duncan and H.J. Beyer >vnd H.Kleinpoppen, Phys. Rev. Lett. 54, 1790 (1985) 4»

19. T. Haji-Hassan and A.J. Duncan and W. Perrie and H.J. Beyer and H. Kleinpoppen, Phys. Lett. A 123, 110 (1987) 20. J.G. Rarity and P.R. Tapster, Phys. Rev. Lett. 64, 2495 (1990)

84 21. F. Selleri and A. Zeilinger, Found. Phys. 18, 1141 (1988) 22. D. Home and F. Selleri, Riv. Nuovo Cimento 14, 1 (1991) 23. T. Haji-Hassan and A.l. Duncan and W. Perrie and H.Kleinpoppen. Phys. Rev. Lett. 62, 237 (1989)

7.3.2 SQUIDs as Macroscopic Quantum Objects

0. Limd Bø and K. Gjøtterud Magnetic flux quantization in a superconducting ring is a well known macroscopic quantum effect. By inserting a Josephson junction in the ring, a Su- perconducting QUantum Interference Device (SQUID) is constructed. The idea is that flux quanta should be able to tunnel into and out of the ring through the Josephson junction. It should in principle be possible to prepare the SQUID in a pure quantum state which is a superposition of macroscopic distinguishable flux states. We have analyzed thought and recti experiments whose aim is to demonstrate such superpositions. One series of experiments is built on A.J. Leggets1) idea of measuring flux as function of time, and looking for quantum tunneling out of a metastable potential well or for quantum coherence in a symmetric double well potential. Severed successful tunneling experiments are reported, but they do not, according to our analysis, seem to be able to distinguish quantum tunneling from classical statistical fluctuation well enough to be convincing. Coher- ence experiments are technically extremely difficult to carry out, and no successful experiments have so far been reported. R.J. Prance et.al.3) have carried out some successful experiments built on another idea. The SQUID is inductively coupled to a classical tank circuit, and its influence on the tank circuits frequency response is measured. The experimental results are claimed to be a demonstration of the validity of the macroscopic quantum model of the SQUID. It seems however from our point of view difficult to interpret any of the reported real experiments as an explicit demonstration of flux superpositions. We will continue our investigation on how a possible flux superposition in SQUIDs could eventually be used as an argument in the context of Schrodinger's cat parado::7).

References:

1. A. J. Legget, I'my. Tin or. I'liys. su/tpl., 69 (1980) 80 2. R. J. Prance, J. E. Mutton, H. Prance, T.D. Clarke, A. Widom and G. Megaloudis, fhhutira I'ln/si,-,, Ada, 56 (1983) 789 3. E. Schrodinger, .\ulurwisM nsrhttjlt it, 23 (1935) 807

85 7.3.3 The Conception of Ether and Phenomena of Light - from Descartes to Einstein

O.Chr. Reistad and O.K. Gjøtterud Our work is a research in the history of ether and light. It is not a story on the history of ether itself and light itself, but a comprehensive work on how ether has played a part in some theories of light. It is to start with Descartes, and continue with particular focus on Newton, Young, Fresnel, Faraday, Maxwell and Einstein. They have all, except for Einstein, done great part of their works on physics with the conception of ether in mind1), and our task is to examine how and why. We are to search for obvious dead ends, and how they are solving/ making problems for theories based on concepts of an ether. Each and every one of the persons mentioned above has his own way in focusing/ overlooking parts of earlier theories2), our task is to examine how and why. As an example one can think of how qualities consequently are ad hoc added to the different conceptions of an ether. We are to examine why and how Einstein removed3) ether with his theories of relativity.

References:

1. G. N. Cantor and M. J. S. Hodge, Conceptions on ether, Cambridge University Press, 1981 2. R. J. Forbes and E. J. Dijksterhuis, A History of Science and Technol- ogy 1 and 2, Penguin Books, Maryland, 1963 3. Albert Einstein, Zum gegenwartigen Stand des Strahlungsproblem, Physikolische Zeitschriften, No. 6, 15. Marz 1909, 10. Jahrgang

86 Chapter 10

Other Fields of Research

8.1 Radiation Physics

8.1.1 Instrumentation for Simultaneous 220Rn and 222Rn Mea- surements

J. Solnørdal*, R. Svendsen", B. Bjerke, F. Ingebretsen and T. Strand. 'Graduate student

Radon originates from two radioactive parent nuclei, 238U and 232Th, giving 222Rn (half-life 3.8d) and 220Rn (56s) respectively. In all but a very few cases, 222Rn is the most abundant isotope in air due to the much longer half-life. However, since the lung dose from the 320Rn daughter products is considerably higher than from the 222Rn daughters, the measurement of the isotope ratio is in many cues necessary for realistic radiation dose calculations.

Dual Ion chanber Dato Logger LASC 1 retar an* «Ni ritar sM valv* LASC 2 LCD PC Deploy

I Control Press.-» i Panel Tenperuv re Hunidrty

Figure 8.1: The dual ion chamber (left) and data logger I/O's and controls.

The present project was started in 1992, primarily as an instrumentation project, with the aim of the design and implementation of equipment for 'in situ' measurements of the isotope ratio and the total activity. The project

87 involves the construction of a dual ion chamber and a flexible datalogger. The general instrumentation idea is shown schematically in fig. 8.1. The two ion chambers, each of 30 1 volume, are coupled together with a 10 m long tube (electrically insulated from the chambers), through which the filtered air is pumped from the outside room, via the first chamber to the second. The chamber currents are measured with LASC units1). The data logger is a "stand alone" compact unit, the main component being a Z80181 microprocessor, and with a 1 Mb RAM. Four analogue inputs and four RS232 I/O ports connects the logger to the two LASCs, an auxiliary PC, and the necessary analogue sensors for various relevant parameters. The PC is connected for testing and programming purpose, and for the retrieval of accumulated data from the logger memory. The I/O drivers are stored in an EPROM.

References:

1. S. Strøm and A. Storruste, Department of Physics Report 89-24, University of Oslo

8.1.2 222Rn and 226Ra in Tap Water from Drilled Wells

T. Strand and B. Lind* "Norwegian Radiation Protection Authority Degassing of radon from tap water has been found to lead to increased indoor concentrations of radon (222Rn) in several countries. High concentrations of radon in tap water (> 1 MBq/m3) are usually associated with deep drilled wells in radium rich granites. Many variables must be considered when assessing the proportion of airborne radon that is derived from a water source. In addition to the concentration of radon in the tap water, these variables include: water-usage rates, air volume, air exchange rate, type of water use and degassing efficiency. Mod- els have been developed to estimate an average value for the air-to-water concentration ratio. In our study, measurements of radon and radium concentrations in tap water were made on samples from 229 and 48 deep drilled wells (70-130 m), respectively, from different parts of Norway. The measurements were performed by liquid scintillation counting. The samples were separated into different categories according to geology of the areas. The results of the study shows that the radon and radium concentrations are more than an order of magnitude higher in samples from granitic than from alum-shale areas. More extensive measurements were made in a few houses. The water-use, and the type of water use (shower, dishwasher, washing machine, etc.) was

88 <90 100 -I .. Ill.l .. ii.. l.i.

kJ/^ oi-n oi-» u-a M-ii M-*I LM

Radon concentration, Bq/a'

Figure 8.3: Radon concentration in the bath room air during showering in one of the houses.

89 recorded as accurately as possible during the one week measurement period. Both continuous (ATMOS-IO pulse ionisation chamber) and passive (CR- 39 etched track detectors) measurements of radon in air were performed in different rooms. The results of the measurements in one of the houses are shown i fig. 8.2. As shown the variation of the radon concentration in indoor air are closely related to the water use. In this house the radon concentration of the tap water and the average concentration in indoor air was 4.3 MBq/m3 and 300 Bq/m3, respectively. Figure 8.3 shows the concentration of radon in the bath room in th? same house during a 30 minute period when the shower was turned on. The radon concentration in the air increased from below 200 Bq/m3 to about 14 kBq/m3. If is assumed that about 30 minutes are spent in the bath-room every day, and that the mean radon concentration during the stay is about 8 kBq/m3, the contribution to the total annual effective dose could be almost 50%. The experimental air-to-water ratios in our study was found to be very close to other published experimental values and to the calculated values based on the single-cell model.

8.1.3 Influence of Meteorological Factors on the Radon Con- centration in Norwegian Dwellings

T. Strand and N.H. Bøhmer- 'Norwegian Radiation Protection Authority In our study, short-term (hours/days) and long-term (months/seasons) vari- ations of the radon concentration in indoor air and influencing factors were investigated. Owing to an increase of the pressure driven flow and a reduction of the ventilation rate, the mean radon concentration in the heating season is usually somewhat higher than in the summer. However, if the foundation walls are of porous material the contribution of diffusion could be of more importance, and the variation pattern somewhat different. Most routine measurements are performed in the heating season and the results are corrected to an annual average by assuming that the measured radon concentration is about twice the level in summer. However, the results of our studies shows that measurements in the spring (March-April) and in the autumn (September-October) are very close to the year average and more or less independent of the variation pattern. These studies will be continued.

90 8.2 General Instrumentation

8.2.1 The Design of a Pure Pitch Automate for Keyboard Instruments

K.E. Skaarberg", F. Ingehretsen and J. Sandstad" "Graduate student "Electronics group

The timed pitch of each individual key in a keyboard instrument has been a problem for musician* and instrument makers for many years. The 12- tone tempered scale that emerged about 300 years ago, turned out to be an acceptable compromise in European music. However, the need for other scales for organs in particular has urged many music theoreticians to look for other solutions. The Norwegian composer Eivind Groven has invented an asynchronous automate for organs that gives a very good approximation to "pure pitch" as well as for other scales used in folk music1). The availability of modern synthesizers as well as fast digital electronics has opened up the possibility to generalize Grovens ideas and his invention. The present project is a development of hardware and software for real time pitch control through the MIDI (Musical Instrument Digital Interface) standard. Furthermore, an analysis of the problem from a physics point of view opens up new musical possibilities. The basis of European music can be found by considering the simultaneous sound (addition) of periodic signals. There are three fundamental intervals; the octave (frequency ratio 1:2), the fifth (2:3), and the third (4:5). These intervals, in turn, yield many of the properties of European music: a) The harmonic scale. b) The frequency ratios of perfect intervals. c) The division of the scale. d) The different temperaments.

The 12-divided octave suggests that 4 fifths should equal 2 octaves plus a third. These two notes were combined to avoid an endless number of pitches and keyboard-instruments unsuitable to human hands. The perfect intervals would differ by 18 millioctaves (mo). This discrepancy could then be divided among the four fifths to keep the thirds perfect (uneven temperament). However, four of the twelve thirds would still be 34 mo too sharp, and restrict possible modulations. A system that makes all intervals sound equally, regardless of the base key, emerged. This system is referred to as even temperament, and is used in all of today's synthesizers. The perfect intervals are statements of mathematical relations, rather than of culture and tradition; they sound "correct". Even-tempered intervals, t< > we ver, can in some cases cause amplitude modulations (beats) (for in-

91 stance close intervals at low frequency). Be- ts are in general considered foreign to the harmonies, and piano music is written so that combinations with the most dominant beats are avoided. Some composers, however, de- liberately use beats as special effects. Although a few composers would prefer absolutely "beat-free" music, the beats might prove to be a powerful dynamic tool if they are controlled. One way to gain some control would be to introduce user- defined intervals; the frequency ratios for a given combination of notes could be pre-programmed. Such a system will enable the playing of the softest major chord and the most extreme diminished chord in the same piece of music. MIDI does not allow for separate tuning of each note played. It does, however, permit separate tuning of each channel. All notes played on a particular channel can be tuned up or down (simultaneously) by using the Pitch Bend (PB) commands. The octaves are kept perfect in even temperament, so it would be sufficient to use twelve channels, independent of how many notes are played simultaneously. The PB commands have a resolution of 14 bits, covering one semitone up or down. This makes thf steps 0,010 mo, which is more than sufficient. Unfortunately, most synthesizers manufactured today interprets PB as 9 bits, giving a resolution of 0,33 mo. This discrepancy may in some situ- ations cause beats, but compared to the 11 mo sharp thirds in the even temperament, this is still a considerable improvement. A PC program for the on-line pitch control has been made, and a dedicated MIDI control unit for this purpose is presently being designed.

References:

1. E. Groven: Temperering og Renstemming. Dreyer Forlag, Oslo (1948)

8.3 Energy Physics

8.3.1 Solar Hydrogen - Hydrogen Produced from Renewable Resources

B. Bjerke, T. Bergene, F. Ingebretseu, J. Rekstad and D. Sultanovic Today's world energy economy is based primarily on fossil fuel energy carriers. Close to 90% of the world's energy consumption is supplied by petroleum, natural gas and coal. Fossil fuel energy carriers have excellent properties like high energy densities, can easily be stored and transported over great distances. Even if fossil fuel energy reserves were to last for a long time, using them causes problems due to their environmental impact. Energy supply for the future with considerable less damage to the environment, can in the long term only be based on renewable energy sources. Today rene» able energy sources like solar irradiance, hydropower and wind

92 energy can only be used directly as heat or electricity due to their inter- mittent nature. However, provided a convenient technology, huge amounts of solar irradiance can be stored as chemical energy in hydrogen that can be produced from water. It can be transported and stored like a fossil fuel. Hydrogen can be used to produce heat or electricity or it can be used as a fuel in transportation. The only residue after combustion is water. A solar hydrogen energy economy makes closed, non-polluting cycles possible. Today's use of hydrogen in large scale is mainly limited as a raw material for the chemical and petrochemical industry. Hydrogen is not used as an energy carrier, except as fuel for rockets (in this application it is not replaceable by any other fuel). There are many possible methods for hydrogen production - both from fossil fuels and from renewable sources. In our group we are oriented towards the use of renewable energy. The goal of our project is to evaluate different methods to produce hydrogen from solar irradiance.

8.3.2 PV-Driven Electrolysis

B. Bjerke, T. Bergene, D. Sultanovic and J. Rekstad We have followed a two-step conversion process - first photovoltaic solarcells converts solar energy to electrical energy and then a water-electrolyzer produces hydrogen. A small experimental system is built by our group f.r.J is shown in fig. 8.4. It consists of a photovoltaic PV-niodule, a 3-cell electrolyzer and a power conditioning unit.

The PV-module is a commercial 60 W with polycrystalline Si-cells. The module (MSX-60 from Solarex) consists of two strings of 18 solarcells connected in parallel and it is fixed mounted. An experimental cooling system of our own construction is integrated in the frame. The purpose of the cooling system is to control the operating temperature of the PV-module. The backside of the module is covered with a 1.5 mm aluminum plate. Three Cu- tubings are thermally connected to the aluminum surface by some aluminum profiles. Heat generated by the solar irradiation is removed by pumping wa- ll,'', ter through the channels. There are different options for the power condition unit. The interface may he done either by fixed direct coupling, by variable direct coupling or by an electronic device (DC/DC) that actively controls the current and voltage levels in order to obtain maximum power transmission. We use the fixed direct coupling in our setup. The electroiyzer is a zero-gap alkaline water-electrolyzer designed and constructed by our group. The electroiyzer is working under normal pressure. The electrode area is 28.3 cm2 and the electrodes are made of pure nickel with no activation. The cell frame is made of clear perspex, so it is easy to watch the gas evolution. Because of the low current densities in the experimental setup, it is necessary to heat the electroiyzer cell to obtain a working temperature up to 80 °C. The heating system consists of two heating elements placed in the electrolyte flow. The temperature is controlled by an external DC-supply. The experimental setup has been tested both in static (for taking characteristics) and dynamic (solar operation) state conditions. The electroiyzer shows an efficiency around 70% (based upon hydrogen higher heating value) at a current density of 0.1 A/cm2. The total efficiency of the system is determined by the ratio between heating value of produced hydrogen and radiation energy on the active solarcell surface. The mean daily efficiency of the total system is close to 7%. We look for possibilities to increase this efficiency. One way for improvements could be by thermal optimization. The efficiencies of the different parts sire dependent of the temperature. The PV-devices work best at low temperatures (the lower the better - down to a maximum efficiency at -150 °C to -100 °C for Si-based cells), the electroiyzer works best at high temperatures (limited by practical numbers depending on technology, 80 °C with our technology). We try to take advantage of these facts by actively cooling the PV-module and heating the electroiyzer. A simulation program has been developed to calculate PV-module efficiency as a function of PV-module temperature and sun insolation. We have made simulations for non-cooled and constant temperature PV-module The daily efficiency of a non-cooled PV-module is 11.2% based on data from a clear summerday in Oslo. The efficiency increases to 13.0% at a PV-module temperature of 10"C and to 13.5% at 0°C. The relative increase of the PV- module efficiency at 10°C is 14%. Another useful effect introduced by the constant operating temperature, is the placement of MPPs (maximumpower point). The MPPs will be placed on a line with slope approx. equal to the slope of the I jV characteristics for an electroiyzer. In fig. 8.5 the placement of the MPPs is plotted for an cooled/non-cooled PV-module. Figure 8.5 shows two different electrolyzers - our own and an advanced KFA- electrolyzer with activated electrodes. It can clearly be seen from fig. 8.5 that it is possible to make a nearly perfect match between a PV-module

94 8.0

7.0

6.0

_< 5.0 o | 4.0 >" CL

~ 3.0

2.0

1.0

0.0 0.0 2.0 4.0 6.0 8.0 10.0 V pv, elec [V]

Figure 8.5: Simulated placements of MPPs as a function of PV-module current/volt age at constant temperature (square dots) and variable temperature (round dots). Also shown I/V characteristics for the ZGE-electrolyzer and the KFA-electrolyzer.

95 and an electrolyzer with direct coupling and thermal control. The I/V characteristics for an electrolyzer is also dependent of the temperature and to obtain a good matching, the temperature should be constant. To try to illustrate the effect of thermal optimization, consider the MPPs for non-cooled and cooled operation corresponding to the highest current at fig. 8.5. The ZGE-electrolyzer will only improve H2- production by a factor of 0.06 when the PV-module is cooled. On the other hand the KFA- electrolyzer will improve H2-production by a factor of 2.8 when cooled. This large variation of improvement shows that the system must be designed to operate at specific temperatures. An advanced electrolyzer will usually not obtain operating temperature in solaroperation mode, but with extra heat supplied and with insulation, it can be operated at a constant temperature. Active heating (ideally taken from solar irradiation) of the electrolyzer unit will bring it to operating temperature and this also reduces its demand for electrical energy during splitting water. The power matching function can be built into the a hydrogen PV-electrolyzer system by controlling the operating temperatures. Such a system will not use a DC/DC-converter and with possible reduced costs as well. The low temperature heat released from the PV-modules could find domestic use or it can be used in a larger scale operation as a fresh water distillery. The lower operating temperature of the PV-devices gives higher efficiencies and a possible longer lifetime as well. The thermal aspects discussed will be further investigated both in theoretical studies and experimentally in the following months.

8.3.3 A Study of Heat-Exchange Properties of a New Semi- Open Solar Collector Concept

D. Sultanovic, B. Bjerke and J. Rekstad Problems related to the flow of thin liquid films and rivulets occur in many important technical applications. A rivulet is a narrow stream of liquid flowing along a solid surface, and sharing an interface with the surrounding fluid. In processes of heat exchange and gas absorption rivulets play a major role, since they have a large surface area to cross-sectional area ratio. This allows for enhanced heat transfer and it is applied in a new semi-open solar collector concept, developed by the group for nuclear and energy physics at the University of Oslo. Although a knowledge of the fluid mechanics and heat transfer in thin liquid films and rivulets is essential in the design of such equipment, a small number of studies in this field have been reported over the past several years, and a great degree of uncertainty exists in understanding of the hydrodynamics ui thin films and rivulets with and without heat transfer.

The purpose of our work is to study heat-exchange properties of the new solar system, investigating changes in heat transfer rates between water

96 le

Figure 8.6: Components of the roof. rivulets and the solid surface of the system for the different flow regimes. Experiments were carried out over a wide range of rivulet flaw rates, Mea- surements of temperatures inside the heat exchange unit of the system, and rivulet widths as the functions of the flow rates were made, so it was possible to calculate the coefficient of heat transfer in each case. The major component of the new solar system is the energy roof which is both a complete roof and a solar collector. Figure 8.6 shows the main components of the roof. It is a sandwich construction with the front absorber plate of polycarbon- ate (or glass), two aluminium plates coupled together (the heat exchange unit), insulation and wind protection. The heat exchange plates are placed directly under the absorber plate, moreover in direct contact with it. The bottom heat exchange plate is corrugated in such a maimer that it comprises channels extending down along the roof. The heat generated by the roof is absorbed by water which flows in these channels in the form of rivulets, not covering the bottoms of the channels with the continuous films. For such a simple geometry, a relatively large number of hydrodynamic regimes can be easily observed, depending on the rivulet flow rates and the characteristics of the solid surface. The transitions between different flow regimes cause changes in heat transfer rates between the water and the solid surface. At low flow rates, most types of rivulets can be described with reference to laminar flow. An increase of the flow rate leads to an increase of the width and the height of the rivulet and the straight laminar rivulet changes to a meandering stream. The transition from linear to meandering rivulet is characterized by the appearance of waves. The characteristics of the rivulet (sinuosity, wavelength and amplitude of the waves) depend on ihe flow rate and the surface slope.

97 A schematic layout of the apparatus is given in fig. 8.7. The central part of the apparatus is an open channel of uniform trapezoidal cross section, sloping at a fixed angle to the horizontal; it is lm long (the dimensions of channel cross section are shown in the figure). The bed of the channel was made from black painted aluminium plate, of thickness 0.5 mm, normally used for roofing, produced by SOLNOR A/S.

valve

Figure 8.7: Experimental apparatus.

Water rivulets were introduced onto the bottom of the channel through a rubber pipe connected to an inlet reservoir. Between the reservoir and the pipe is a manual control valve. The flow rate was measured manually by rate of fall from the water supplying pipe in a burette. The downstream end of the channel is a receiving reservoir. The bed of the channel was heated by warm water which was flowing through copper pipes, glued to the bottom of the aluminium plate at each of the sides of the channel, providing isothermicity of the bottom of the channel. No insulation was used in the system.

The experimental procedure consisted of flowing the rivulets over the bottom of the channel at a constant flow rate until the temperatures obtained a steady state values. Measurements of temperature of the bottom of the channel were made at three positions along the channel: temperature of water entering the channel was measured at the bottom of upstream reservoir and temperature of water leaving the channel was measured at the top of downstream reservoir. These temperatures, together with the flow rate, constituted one set of data. Rivulet width measurements as a function of liquid flow rate, were also conducted at a number of positions along the channel and then calculated the average values. The data acquisition system was based on LAB VIEW. That is a software package designed for data collection, data analysis and data presentation. For the temperature measurements platinum sensors (Pt-100) were used. They were coupled to the Macintosh computer by a current-loop (4-20 mA). The results of these measurements will be very useful in getting a better understanding of such phenomena. They are to be published in Solar Energy magazine.

8.3.4 Photolysis- Hydrogen Produced Directly by Solar Ra- diation

T. Bergene and J. Rekstad We evaluate the possibility of producing hydrogen directly by solar illumination without going through the step of electrolysis. One problem is that water is transparent at wavelengths representative for the sunlight. This necessitates the use of some catalyzing process or substance. One method is the use of semiconductor material as a catalyzing substance. We call this process photolysis1). So far efficiencies of up to 8-10% have been achieved in experiments. This is far below the maximum theoretical thermodynamical limit of about 30%, and also requires the use of very expensive semiconductor material. But it is very promising compared to current silicon solar-cell technology, which at maximum have achieved a conversion efficiency of sunlight to electricity of 8-15%, taking into account the continuous and intensive research on the latter process2). The basic principles of photolysis are well understood, but there are several difficulties to be overcome in order to raise the efficiency further. Key words in that respect are: a) corrosion of the electrodes, b) appropriate choice of semiconductor material in order to match band-gap, flat-band potential and red-ox levels present in the electrolyte, c) charge transfer through the semiconductor-electrolyte interface and d) recombination losses (of electrons and holes), both in the bulk of the semiconductor and at the interface. We have started an analysis of efficiency determining parameters. We investigate what would be a realistic efficiency limit considering all relevant loss-factors. In that respect, our conclusion is that the photolyii® process can compare with the PV-electrolysis process. But for the photolysis process, the practical problems are far from being solved. So we conclude that at the present time the PV-electrolysis system is the most favourable. During our work we have realized that an adequate understanding of the physical processes occurring in the layer between the semiconductor and

99 the electrolyte is non-existent. Some theories based on a phenomenological approach exist, but a fundamental understanding would be highly desirable. We would like to give substantial contributions to such an understanding, and so far we have investigated quantization effects occurring in the depletion layer (band bending area). Quantization is a result of confinement and boundary conditions given by the interface itself and the bulk of the semiconductor, and as a result, the minority charge carriers can only be injected into the electrolyte from discrete energy levels. If now the semiconductor surface is covered by some protective layer (Au, Si02, etc.) in order to avoid corrosion, trapping of these charge carriers can occur if the band edge is placed at a lower energy level than the red-ox potential in the electrolyte. In that way chemical reactions which is thermo- dynamically forbidden can take place. We are particularly interested in the possibility for oxygen evolution at an n-GaAs electrode during illumination, a process which is forbidden. We want to give a correct kinematic picture of what is happening in the photolysis process and want to suggest possible experimental set-ups in order to achieve higher efficiencies.

References:

1. T. Bergene, University of Oslo Report, UiO/PHYS/92-17/1992 2. T. Bergene, Technical Review Weekly, 2, 16-17 (1993) (in Norwegian)

8.3.5 The Possibility for Combined Quantum/Thermal Con- verters

T. Bergene, B. Bjerke and J. Rekstad There are two fundamentally different types of solar energy converters. One is the thermal converter where heat is generated from the solar radiation. The other is the quantum converter which in our context means solar cells. The photolysis of water and the photosynthesis in green plants are also to be considered as quantum conversion processes. Solar cells act as solar heat collectors, and during operation they can become very hot. This is a result of the fact that if the efficiency of the solar cells are 10 %, only 10 % of the solar energy is carried away during the quantum conversion process. 90 % of the solar energy appears as heat in the system. We have investigated the temperature dependence of solar cells and found that the efficiency increases by 0.05 % /°K. For a realistic temperature difference of 30 °K (cooling) this means an increase of 1.5 %, or a relative increase of 15 % (initial efficiency of 10 %). Removing heat thus have a positive feedback on the solar cells, and this low-temperature heat can be utilized in different systems.

100 So far we have done a theoretical study and calculated in detail the physical consequences of this combination or integration. The results are promising. During the summer of 1993 an experimental study will take place.

8.3.6 The Importance of Insolation Autocorrelation in Solar Heat System Calculations

F. Tngebretsen A previously1) described PC simulation program for the SOLNOR (and similar) solar heating system has been further developed. In this program, an empirical day- to day insolation autocorrelation is used. The program has been used to study some general features and expected behaviour for the SOLNOR solar heating system in Norway. The most frequently used computer programs for the design and performance calculations of solar energy systems in Norway are based on time averaged insolation values, the averaging periods usually being one month. However, since the efficiency of a solar collector depends on the insolation I (ex J"1), the use of average insolation values will underestimate the available solar energy if the stable insolation periods (autocorrelation) are considerably shorter. This is indeed the case for the northern European climate. In Norway the average period lengths are 2-5 days only. The most comprehensive and accurate average insolation values for various parts of Norway have been published by Olseth and Skartveit2). Their annual integrated insolation duration is compared with simulated values in fig. 8.8. The agreement is very good for insolation >80 W/m2. Active solar heating systems, including the SOLNOR system, does not yield useful energy below a cutoff /-value of 150 - 200 W/m2. The total insolation and integrated duration is correctly reproduced by the program for the relevant /-values. The importance of the use of realistic insolation period lengths is demon- strated in fig. 8.9. Here, the solar energy contribution to water and space heating for a well insulated house in the Oslo area is calculated for different water storage volumes. The calculations are performed both with monthly avdage and with simulated insolation values. The figure shows that there is no significant solar energy gain for water storage volume greater than about 2 m3. Furthermore, the "average" calculation gives a maximum solar energy contribution of about 40%, whereas the simulation gives more than 50%. The optimum water storage volume corresponds approximately to an energy storage for the average day- to day insolation periods. Calculations for larger storage volume up to 20m3 show no significant increase in the energy gain. Well above this limit, not shown in the figure, the effect of a long term seasonal storage will increase the total annual solar energy gain. However, this storage volume (as 50 — 100m3) is not realistic for a single house.

101 4500

4000 3500

3000 Simulated

1 22515 - CS-Data

2CGJ

1500

500 0 it >0 >40 >80 >150 >250 >350 >450 >600 >800 >20 >60 >100 > 200 > 300 >400 >500 >700 Irradiation

Figure 8.8: Simulated integrated duration distribution for various insolation lower limits (W/mJ), compared with values from ref.J)

rø Water and heal solar contribution

•

30 - — Average SO --- Simulated IQ i

9 10 Water storage

Figure 8.9: Calculated solar hot water and space heat contribution for a house in the Oslo region. For the broken curve the insolation autocorrelation is simulated.

102 References:

1. F. Ingebretsen: "Simulated Solar Heat from the SOLNOR System". Nuclear and Energy Physics Annual Report 1991, University of Oslo Report, UiO PHYS 92-09, section 8.2.2, and Proceedings of the NORTH SUN '92 conference, Trondheim 24-26 June 1992, p. 351

2. J.A. Olseth and A. Skartveit: "Varighetstabellar for timevis solstråling mot 11 flater på 16 norske stasjonar". Meteorological report series, University of Bergen, 1 1987

8.4 Neural Network

K.I. Isachsen, J.Å. Westberg, T. Engeland and I. Espe

Neural Networks, or Neurocomputing, is a new approach to information processing. A Neural Net is constructed of simple processing elements, neurons, exchanging information through connections. They are controlled through the so-called weights. As a result we get a system with the ability to learn, to predict and to recognize learned patterns. Neural nets have proved to be very useful in a number of cases. Examples are financial predictions, decision making, pattern recognition, process controls, future predictions, medical diagnosis etc.. An underwater listening system developed by General Dynamics is a good example what a neural network can do. This system is able to identify different types of ships and submarines by the sound of their engines. Similarly, a network has been developed that are able to distinguish among different aircraft. It can identify an aircraft based on as little as 10 % of full description. Neural nets may be implemented on conventional computers. This simulates parallel processing of a neural net in a sequential computer. Program of this type is often called Neural Network Simulators and is available in the market. Lately neural network has been designed on electronic chips. Then electronics around the chip control the dataflow. The present fastest chip is Intels 80170NX Electrically Trainable Analog Neural Network (ETANN) chip. Inputs and outputs to this chip are analog and thus suited to real- world application. In our laboratory a system has been set up around a hardware and software developers system delivered by Intel cooperation. The Intel neural network training system (iNNTS), is a complete environment for training and testing the 80170NX chips. After collecting and preprocessing of data, it can set up and simulate a network system in software. After successful training session the simulated weights are download on a 80170NX chip and one can perform a chip-in-ioop optimization to accommodate the fabrication variances in each chip. With the chip in loop it is then possible to test the network to see how well it works.

103 After training the chip may be embedded in a stand-alone system, developed by users. One 80170NX contains 64 analog neurons and supports two-layer neural networks trained with backpropagation or recurrent backpropagation learning laws. Input are organized in two groups, external and recurrent, each containing 80 x 64 weights and bias inputs. Due to output buffer control one chip is able to support a two-layer mapping of 128 inputs to 64 outputs. Two students are at the moment involved in research on how neural nets learn and how to optimize the learning process. A learning process consist of representing input vectors from a training set to a network, one at a time. At each step one measures how well the net performs and the goal is to minimize the average error over all training patterns. It is essential that the trained network is able to generalize, that is to predict correctly the output in cases where the input does not belong to the training set. By studying relatively simple systems we hope to get information about the learning process and thereby improve the learning speed and the efficiency on more complicated systems. It is also desirable to use as few units as possible in a net. This will reduce cost and training time. Too many units may reduce the networks capability to generalize. The group has been working on approaches where the size of the networks grows during the learning process in order to solve the problem at hand. Our group is at the moment concentrated on a few projects. Two students are in the early stage in developing a network which can read inputs of written text. The network should produce a code for the word sounds that can be translated by electronics into sounds in a speaker. The net shall learn by experience and not by rules or from a dictionary. This project includes writing a network simulator which makes it possible to study more general network aspects. Included are also an exploration of Intels development set INNTS. In a second project we concentrate on neural networks ability to predict future values of time series by extracting knowledge from the past. As a part of this project we analyze noise removal from experimental time series. Past and future behaviour of sunspots is a classical problem of this type.

104 Chapter 10

Seminars

Date: 6.01 F. A. Gareev: Cross Stucture of Resonance Spectra. 14.01 M. Guttormsen: Erfaring med nytt opplegg for FYS-270 høsten 1991. 4.02 T. Tveter: Kaos og K-kvantetallet. 18.02 T. Tveter: Kaos og K-kvantetallet. 25.02 V. Zelevinsky: One-body chaos and many-body chaos in nuclear physics. 10.03 E. Staubo: Kjernematerie under ekstreme betingelser. 7.04 B. Shukhman: Some applications of quasi-random points in monte-carlo algorithms. 28.09 M.V. Zukov: Physics of the halo nuclei. Light radioactive nuclei: Theory and experiment. 20.10 S. Messelt: Åpning av den nye syklotronen i Jyvaskylå. 20.10 G. Løvhøiden: Rapport fra konferensen: Nuclear Structure and Nuclear Reaction at Low and High Intermediate Energies. Dubna, sept. 15-19 1992 8.12 B.Bjerke og T. Bergene: Status quo for solenergibasert hydrogenproduksjon i Tyskland og Norge og en orientering om vårt engasjement innen området.

105 Chapter 10

Committees, Conferences and Visits

10.1 Committees and Various Activities

External committees and activities only are listed.

B. Bjerke: Member of IEA working group: Annex IX Photovolatic Elec- trolyzer Test Facilities. T. Engeland: Referee for Nuclear Physics and Physics Letters.

K. Gjøtterud: Referee for Nuclear Physics and Physica Scripta. Member of the committee for The Lisl and Leo Eitinger price. Member of The Norwegian Physical Society's Human Rights Committee. Member of "International Federation of Scientists for Soviet Refusniks". Representative of the Faculty of Mathematics and Natural Sciences in the Council for Examen Philosophicum. M.Guttormsen: Member of the Board of the Nuclear Physics Committee of the Norwegian Physical Society. Deputy Member of the National Committee for Nuclear Re- search. Referee for Nuclear Physics and Zeitschrift fiir Physik.

106 T. Holtebekk: Chairman of The Norwegian Standardization Organization Sub-Committee for Technical and Physical Units. Member of the Norwegian Research Council advisory committee for evaluation of new generation equipment for radio- carbon dating. F. Ingebretsen: Member of the Science Council of the Norwegian Research Council for Science and Humanities. Chairman of the Science Council Physics committee. Member of the CERN committee. Member of the Norwegian EISCAT board. Editor of the periodical "Fra Fysikkens Verden". Member of an advisory committee for the Research Council project: "Women in and after the science education period". Member of the Board of Directors of SOLNOR A/S (until Aug. 1992). Member of the advisory committee for the "SOLIS" project: Solar energy in the school. G. Løvhøiden: Member of the CERN SPS and LEAR Committee. Member of the Norwegian Advisory Committee for the RPP program in EEC. Referee for Nuclear Physics. Member of the Norwegian Academy of Science and Letters. E. Osnes: Member of the Council and Executive Committee of the Eu- ropean Physical Society. Member of the EPS Action Committee on Publications. Member of the Nuclear Physics European Collaboration Committee (NuPECC). Member of the Executive Board of NORDITA. Member of the Advisory Committee of Nuclear Physics of NORDITA. Chairman of the Norwegian Committee for Nuclear Re- search (NUK) under NAVF. Co-editor (with T.T.S. Kuo) of International Review of Nu- clear Physics, published by World Scientific Publ. Comp.. Referee for Nuclear Physics, Physics Letters B and Physica Scripta. Member of the Norwegian Academy of Science and Letters, and of the Royal Norwegian Society of Sciences and Letters. Honorary Member of the Norwegian Physical Society.

107 J. Rekstad: Member of the Board of Directors of NAVF. Member of the National Committee for Nuclear Research (NAVF). Member of the Board of Directors of "International Cardio- logical Institute for Therapeutic Research". Member of a Solar House Committee in Østfold Fylke. Member of the Council of KREANOVA, Material Technol- ogy Network Center in Haugesund. Referee for Nuclear Physics. Chairman of the Board of Directors of SOLNOR A/S. Member of the Board of Trustees (bedriftsforsamling) of Orkla-Borregaard A/S.

R. Tangen: Member of the Norwegian Academy of Science and Letters.

P.O. Tjøm: Referee for Nuclear Physics.

10.2 Conferences

The Section of Nuclear Physics and Energy Physics participated in the An- nual Meeting of the Norwegian Physical Society, Stavanger, June 1992. L. Berholt, L. Henden, M. Guttormsen, A. Holt, E. Koksvik, S. Messelt, F. Ingebretsen, J. Rekstad, P. O. Tjøm and T. S. Tveter participated in the 7th Nordic Meeting on Nuclear Physics, Vigsø Kursuscenter, Denmark, A j-^ast 17 - 21, 1992. M. Guttormsen participated in Euroball Meeting on Auxiliary Detectors and Selective Devices, HMI, Berlin, June 1 - 3, 1992. M. Guttormsen and G. Løvhøiden participated in the CHIC Spring Meet- ing, Oslo, May 14 - 16, 1992. T. Holtebekk participated in the IVth ESSAT Conference: Origins, Time and Complexity in Science and Theology, Rome, March 23 - 28, 1992. F. Ingebretsen participated in the "North Sun" solar energy conference, June 24-26, Trondheim; in the "Solis" meeting, Dalen, Telemark; and as observer in the XXIII international physics olympiad, Helsinki, July 5 - 13, 1992. G. Løvhøiden participated and gave an invited talk at the International Conference on Nuclear Structure and Nuclear Reactions at Low and Inter- mediate Energies, Dubna, Russia, September 15 - 19, 1992. B. Bjerke participated in Hydrogen 92 - 9th World Hydrogen Energy Con- ference, CNIT, Paris, France, June 22 - 25, 1992.

108 M. Hjorth-Jensen and E. Osnes participated in the International Nuclear Physics Conference, Wiesbaden, July 26 - August 1, 1992 E. Osnes participated and gave invited talks at the International Workshop on Nuclear Structure Models, Oak Ridge, March 16 - 25, 1992 and the International Workshop on Microscopic Nuclear Theory, Seattle, September 14 - 18, 1992

109 Chapter 10

Theses, Publications and Talks

11.1 Theses

A. Haugan: Realistic shell model calculations of log(ft)-values in pf-shell nuclei. Cand. Scient. Thesis L. Bergholt: Methods for the determination of 7-multiplicity for the crystal ball CACTUS. Cand. Scient. Thesis

11.2 Scientific Publications

11.2.1 Nuclear Physics and Instrumentation

H.E. Andås Bell's Inequalities for Quantum Mechanics Phys. Lett. A16T, 6, 1992.

M. Hjorth-Jensen, E. Osnes and H. Miither Folded-Diagram effective interaction with the Bonn meson-exchange potential model Annals of Physics 213, 102, 1992.

M. Hjorth-Jensen, M. Borromeo, H. Miither and A. Polls Isobar contributions to the imaginary part of the optical-mode potential for finite nuclei Nucl. Phys. A550, 1992.

M. Hjorth-Jensen, T. Engeland, A. Holt and E. Osnes On the Role of Third- and Higher-Order Contributions to the Effective In- teraction for pf-Shell Nuclei Nucl. Phys. A541, 105, 1992.

110 M. Hjorth-Jensen, E. Osnes and T.T.S. Kuo Effective interactions for valence-hole nuclei with modern meson-exchange potential models Nucl. Phys. A540, 145, 1992.

M. Piiparinen, A. Ataq, G. de Angelis, S. Forbes, N.Gjørup, G. Hage- mann, B. Herskind, F. Ingebretsen, H. Jensen, D. Jerrestam, H. Kusakari, R. Lieder, G.M. Marti, S. Mullins, J. Nyberg, D. Santonocito, H. Schnare, G. Sletten, K. Strahle, M. Sugawara, P.O. Tjøm, A. Virtanen and R. Wadsworth High Spin Level Structure of 143Eu Zeitschrift fiir Physik A, 343, 367-368, 1992.

E. Andersen, G. Løvhøiden and the NA36 Collaboration Strangeness production at mid-rapidity in S+Pb at 200 GeV/c per nucleon Phys. Lett. B294, 127, 1992.

E. Andersen, G. Løvhøiden and the NA36 Collaboration Results from CERN experiment NA36 on strangeness production Nucl. Phys. A544, 309c, 1992.

E. \ndersen, G. Løvhøiden and the NA36 Collaboration A high speed fastbus VME data acquisition system for the CERN NA36 experiment Nucl. Instr. Meth. A320, 300, 1992.

E. Andersen, G. Løvhøiden and the NA36 Collaboration Target dependence of central rapidity lambda production in sulfur-nucleus collisions at 200 GeV/c per nucleon Phys. Rev. C46, 727, 1992.

M.J.G. Borge, G. Løvhøiden et al. On the nuclear structure of 229Ra Nucl. Phys. A539, 249, 1992.

W. Kurcewicz, G. Løvhøiden et al. The nuclear structure of 223Fr Nucl. Phys. A539, 451, 1992.

E. Andersen, H. Helstrup, G. Løvhøiden, T.F. Torsteinsen, M. Guttormsen, S. Messelt, T.S. Tveter, M.A. Hofstee, J.M. Schippers and S.Y. van der Werf Helium induced one-neutron transfer to levels in 162Dy Nucl. Phys. A550 235-249,1992.

L.P. Csernai, G. Fai. C. Gale and E. Osnes Momentum-Dependent Mean Field and the Nuclear Equation of State Phys. Rev. C46, 736, 1992.

E. Osnes and D. Strottman Spin-Tensor Analysis of Realistic Shell-Model Interactions Phys. Rev. C45, 662, 1992.

Ill 11.2.2 Radiation Physics

T. Strand and N.H. Bøhmer Influence >f Meteorological Factors on the Radon Concentration in Norwe- gian Dwellings Proc. of the International Symposium on Radon and Radon Reduction Tech- nology, Minneapolis, USA, September 22-25, 1992.

T. Strand and B. Lind Radon in Household Water from Deep Bored Wells in Norway Proc. of the International Symposium on Radon and Radon Reduction Tech- nology, Minneapolis, USA, September 22-25, 1992.

R.T. Lie, L.M. Irgens, R. Skjærven, J.B. Reitan, P. Strand, and T. Strand Birth Defects in Norway by Levels of External and Food-based Exposure to Radiation from Chernobyl American Journal of Epidemiology, vol.126, no.4, 1992.

11.2.3 Energy Physics

J. Rekstad and M. Mehlen Improvements in Solar Heat Collector Roofs International Patent, PCT, N0/00072, August 1992.

J. Rekstad and M. Mehlen Fremgangsmate for å fjerne varme fira et solfangertak, samt anordning for utøvelse av fremgangsmate Norsk patent NO 170698 C, Styret for det industrielle rettsvern, august 1992.

J. Rekstad Elementbereder med hevertkoplinger Norsk patent NO 171236 B, Styret for det industrielle rettsvern, november 1992.

11.3 Scientific and Technical Reports

11.3.1 Nuclear Physics and Instrumentation

H.E. Andås Bell-type Experiments and The Concept of Locally Stochastic Causality University of Oslo Report UiO PHYS 92-25 1992.

H.E. Andås Quantum Theory and Questions of Reality and Completeness Thesis for the Degree of Doctor Scientiarum, Oslo, December 1992.

112 H.E. Andås and O.K. Gjøtterud Quantum Theory find Questions of Reality and Completeness University of Oslo Report UiO PHYS 92-24, 1992.

L. Engvik, M. Hjorth-Jensen and E. Osnes Model-Space Nuclear Matter Calculations with the Bonn Potential University of Oslo Report, UiO PHYS 92-30, 1992.

M. Guttormsen (editor) CHICSI, a proposal for a multidetector AE-E particle telescope University of Oslo Report, UiO PHYS 92-02 1992.

M. Guttormsen SHU, a proposal for a multidetector AE-E particle telescope University of Oslo Report, UiO PHYS 92-21 1992.

V.A. Avdeichikov, A.I. Bogdanov, C.V. Lozhkin, Yu.A. Murin, M. Berg, L. Carlén, R. Elmer, R. Ghetti, B. Jatobsson, B. Norén, H. Ryde, A. Oskarsson, H.J. Whitlow, J.P. Bondorf, K. Sneppen, M. Cronqvist, O. Skepp- stedt, C. Ekstrom, G. Ericsson, L. Westerberg, M. Guttormsen, S. Kox, F. Merchez, D. Rebreyend, J. Julien, G. Løvhøiden, K. Nybø, T.F. Thorstein- sen, S. Mrowczynski and S. Pratt pp-, nn- and np Interferon-etry in 30A MeV Reactions Cosmic and Subatomic Physics Report LUBP 9201, 1992.

J. Rekstad, M. Guttormsen, T.S. Tveter og L. Bergholt Kjernefysiske problemstUlinger ved Syklotronlaboratoriet University of Oslo Report, UiO PHYS 92-10 1992.

J. Rekstad T.S. Tveter, M. Guttormsen and L. Bergholt The K-dependence in the gamma-decay of neutron resonances in 168Er and l78Hf University of Oslo Report, UiO PHYS 92-23 1992.

M. Hjorth-Jensen, M. Borromeo, H. Miither and A. Polls Isobar contributions to the imaginary part of the optical-model potential for finite nuclei Univ. of Oslo Report UiO PHYS 92-08

M. Hjorth-Jensen, M. Kirchbach, D.O. Riska and K. Tsushima Nuclear renormalization of the isoscalar axial coupling constants University of Helsinki Report HU-TFT-92-49

M. Hjorth-Jensen, T. Engeland, A. Holt and E. Osnes Perturbative many-body approaches to finite nuclei Univ. of Oslo Report UiO PHYS 92-22

E. Osnes, M. Hjorth-Jensen, T. Engeland and A. Holt Shell model calculations with realistic effective interactions Univ. of Oslo Report UiO PHYS 92-32

113 T. Engeland, M. Hjorth-Jensen, A. Holt and E. Osnes The structure of the neutron deficient Sn isotopes Univ. of Oslo Report UiO PHYS 92-41

M. Hjorth-Jensen, T. Engeland, A. Holt and E. Osnes Perturbative Many-Body Approaches to Finite Nuclei University of Oslo Report, UiO PHYS 92-22, 1992.

T. Holtebekk, E. Osnes, J. Rekstad og S.O. Sørensen Festskrift til Roald Tar gen i anledning hans 80-års dag 8 februar 1992 University of Oslo Report, UiO PHYS 92-33 1992 25.

B. Herskind, T. Døssing, S. l eoni, M. Matsuo, E. Vigezzi, A. Ata$, M. Berstrom, A. Bracco, A. Brocksted, H. Carlsson, P. Ekstrom, H.J. Jensen, J. Jongman, G.B. Hagemann, F. Ingebretsen, R.M. Lieder, T. Lonnroth, A. Maj, B. Million, A. Nordlund, J. Nyberg, M. Piiparinen, H. Ryde, M. Sug- awara, P.O. Tjøm, A. Virtanen A Trace of Motional Narrowing ? Contribution to Int. Conf. on Nuclear Structure at High Angular Momen- tum, Ottawa, May 18-23, 1992 and 7th Nordic Meeting on Nuclear Physics, Book of abstracts p. 102, Vigsø Kursuscenter, Denmark 17.-21. August 1992.

E. Andersen et al. International Conference on Nuclear Structure and Nuclear Reactions at Low and Intermediate Energies Dubna, Russia, September 15-19, 1992.

V.K. Mishra, G. Fai, L.P. Csernai and E. Osnes Thermal Properties of Nuclear Matter with a Momentum-Dependent Effec- tive Interaction Report KSUCNR-007-92, Center for Nuclear Research, Kent State Univer- sity, 1992.

P.A. Amundsen, A. Bøe, H. Carlsen, A.G. Ellingsen, T. Espedal, T.I. Ped- ersen, T. Refvem, J. Rekstad, R. Risnes, L. Storesletten and K. Am Plan for sivilingeniørstudiet i tekniske realfag ved Høgskolesenteret i Roga- land Arbeidsgrupe oppnevnt av Kollegiet for Sivilingeniørutdanningen ved HSR, Stavanger, 10 november 1992.

J.C. Wikne A CAMAC 32-Channel Pile-Up Detection and Rejection Module University of Oslo Report UiO PHYS 92-28 1992.

T. Bergene, B. Jensen, R. Jensen og A. Næss En samtale om fysikk, fysikere og menneskelig væren. University of Oslo Report, UiO PHYS 92-38, 1992.

114 11.3.2 Energy Physics

T. Bergene Hydrogen Production from Solar Energy; A Review of Photolysis University of Oslo Report, UiO PHYS 92-17, 1992.

11.3.3 Educational Physics

C. Angell, A. Isnes Videreutvikling av læringsmiljøet ved Fysisk institutt. FYS 112 University c/ Oslo Report UiO PHYS 92-06 1992.

11.4 Scientific Talks

11.4.1 Nuclear Physics and Instrumentation

H.E. Andås Einstein og kvantemekanikken etter EPR-avhandlingen 1935 Dr. scient.-seminar, Fysisk institutt, UiO, 12-92.

H.E. Andås Målebeskrivelsen i Kvantemekanikken Dr. scient .-seminar, Fysisk institutt, UiO, 11-92.

K. Gjøtterud "The New Physics." Forelesning Sykepleievitenskapelig Symposium Voksenåsen Kultur- og Kon- feransehotel Oslo 02.04.92.

V.A. Avdeichikov, A.I. Bogdanov, O.V. Lozhkin, Yu.A. Murin, M. Berg, L. Carlén, R. Elmér, R. Ghetti, B. Jakobsson, B. Norén, H. Ryde, A. Os- karsson, H.J. Whitlow, J.P. Bondorf, K. Sneppen, M. Cronqvist, O. Skepp- stedt, C. Ekstrom, G. Ericsson, L. Westerberg, M. Guttormsen, S. Kox, F. Merchez, D. Rebreyend, J. Julien, G. Løvhøiden, K. Nybø, T.F. Thorstein- sen, S. Mrowczynski and S. Pratt pp-, nn- and np Interferometry in 30A MeV Reactions The 8th Winter Workshop on Nuclear Dynamics, Jackson Hole, Wyoming, USA, Jan. 19 - 24, 1992.

M. Guttormsen The SIRI and CHICSI Particle Telescope Projects EUROBALL Meeting on Auxiliary Detectors and Selective Devices, HMI, Berlin, June 1 - 3, 1992, Slide Report p. 92

115 E. Andersen, H. Helstrup, G. Løvhøiden, T.F. Thorsteinsen M. Guttormsen, S. Messelt, T.S. Tveter, M. Hois tee, M. Schippers, S.Y. van der Werf Low Spin S-Band Members in 1001G2Dy Int. Nuclear Physics Conference, July 26 - August 1, 1992, Wiesbaden, Germany Book of Abstracts, p. 1.2.53

E. Andersen, H. Helstrup, G. Løvhøiden, T.F. Thorsteinsen, M. Guttorm- sen, S. Messelt, T.S. Tveter, M.A. Hofstee, J.M. Schippers, S.Y. van der Werf Low spin S-band members in 1601CJDy The International Conference on Nuclear Structure and Nuclear Reactions at Low and Intermediate Energies, Dubna, Russia, September 15-19, 1992.

M. Guttormsen, J. Rekstad, L. Bergholt, F. Ingebretsen, G. Løvhøiden, S. Messelt and T.S. Tveter Oscillatory Behaviour of 7-Ray Multiplicity 7th Nordic Meeting on Nuclear Physics, Book of abstracts p. 24, Vigsø Kursuscenter, Denmark 17.-21. August 1992.

T.S. Tveter, L. Bergholt, M. Guttormsen and J. Rekstad The K Quantum Number and the Decay of Neutron Resonances 7th Nordic Meeting on Nuclear Physics, Book of abstracts p. 26, Vigsø Kursuscenter, Denmark 17.-21. August 1992.

L. Bergholt, M. Guttormsen, J. Rekstad and T.S. Tveter Extraction of Multiplicity Distributions 7th Nordic Meeting on Nuclear Physics, Book of abstracts p. 105, Vigsø Kursuscenter, Denmark 17.-21. August 1992.

M. Hjorth-Jensen Invited talk given at the "Realistic Nuclear Structure" conference, Stony Brook, May 28-30 1992, USA

M. Hjorth-Jensen, T.T.S. Kuo and E. Osnes Folded Diagrams and the Quenching of Spin Matrix Elements International Nuclear Physics Conference, Wiesbaden, Germany, 26 July - 1 August 1992, Book of Abstract, ed. U. Grundinger, 1992, p. 1.3.11.

G. Zwartz, H.R. Andrews, M. Cromaz, T.E. Drake, A. Galindo-Uribarri, F. Ingebretsen, V.P. Janzen, S.M. Mullins, L. Persson, T. Porcelli, D. Prévost, D.C. Radford, J.C. Waddington and D. Ward Search for Superdeformed Nuclei in the A=190 Region Contribution to Int. Conf. on Nuclear Structure at High Angular Momen- tum, Ottawa May 18-23, 1992.

116 A. At as, M. Piiparinen, B. Herskind, J. Nyberg, G. de Angeli?, S. Forbes, N. Gjørup, G. Hagemann, F. Ingebretsen, H. Jensen, D. J err est am, 'rl. Kusakari, R. Lieder, G.M. Marti, S. Mullings, D. Santonocito, H. Schnare, G. Sletten, K. Strahle, M. Sugawara, P.O. Tjøm, A. Vir tanen and R. Wadsworth Decay out of a Superdeformed Band in 143Eu Contribution to Int. Conf. on Nuclear Structure at High Angular Momen- tum, Ottawa, May 18-23 1992, and 7th Nordic Meeting on Nuclear Physics, Book of abstracts, Vigsø Kursuscenter, Denmark 17.-21. August 1992.

M.Piiparinen, A. At as, G. de Angelis, S. Forbes, N.Gjørup, G. Hagemann, B. Herskind, F. Ingebretsen, H. Jensen, D. Jerrestam, H. Kusakari, R. Lieder, G.M. Marti, S. Mullins, J. Nyberg, D. Santonocito, H. Schnare, G. Sletten, K. Strahle, M. Sugawara, P.O. Tjøm, A. Virtanen and R. Wadsworth High Spin Level Structure of 143Eu Contribution to Int. Conf. on Nuclear Structure at High Angular Momen- tum, Ottawa, May 18-23 1992.

A. Atag, M. Bergstrom, A. Bracco, A. Brockstedt, H. Carlsson, L.P. Ekstrom, J.M. Espino, H.J. Jensen, G.B. Hagemann, B. Herskind, A. Gripmark, F. Ingebretsen, J. Jngman, S. Leoni, R.M. Lieder, T. Lonnroth, A. Maj, B. Million, A. Nordlunf, J. Nyberg, M. Piiparinen, H. Ryde, M. Sug- awara, P.O. Tjøm, A. Virtanen Low-energy Transitions for Angular Correlation Data for 1G3Tm 7th Nordic Meeting on Nuclear Physics, Book of abstracts p. 90, Vigsø Kursuscenter, Denmark 17.-21. August 1992.

H.J. Jensen, G.B. Hagemann, P.O. Tjøm, A. Atas, M. Bergstrom, A. Bracco, A. Brockstedt, H. Carlsson, P. Ekstrom, J.M. Espino, B. Herskind, F. Ingebretsen, J. Jongman, S. Leoni, R.M. Lieder, T. Lonnroth, A. Maj, B. Million, A. Nordlund, J. Nyberg, M. Piiparinen, H. Ryde, M. Sugawara and A. Virtanen Delayed Band Crossing in the Unfavoured Signature Partner of the h9/ >[541]l/2~ Band in 163Tm Contribution to Int. Conf. on Nuclear Structure at High Angular Momen- tum, Ottawa, May 18-23 1992, and 7th Nordic Meeting on Nuclear Physics, Book of abstracts p. 104 Vigsø Kursuscenter, Denmark 17.-21. August 1992.

S. Leoni, T. Døssing, B. Herskind, M. Matsuo, E. Vigezzi, A. Atas, M. Bergstrom, A. Bracco, A. Borgstedt, H. Carlsson, P. Ekstrom, H.J. Jensen, J. Jongmann, G.B. Hagemann, F. Ingebretsen, R.M. Lieder, T. Ionnroth, A. Maj, B. Million, A. Nordlund, J. Nyberg, M. Piiparinen, H. Ryde, M. Sug- awara, P.O. Tjøm, A. Virtanen Spin Dependence of Rotational Damping by the Rotational Plane Mapping Method Contribution to Int. Conf. on Nuclear Structure at High Angular Momen- tum, Ottawa may 18-23 1992 and 7th Nordic Meeting on Nuclear Physics, Book of abstracts p. 100, Vigsø Kursuscenter, Denmark 17.-21. August 1992.

117 I. Sakrejeda, G. Løvhøiden and the NA36 Collaboration CERN experiment NA36 - an example of the search for quark gluon plasma in relativistic heavy ion collisions APS Spring Meeting, Washington DC, April 20-23,1992.

R. Zybert, G. Løvhøiden and the NA36 Collaboration Strangeness production in 32S+Pb collisions at 200 GeV/n XXVHth Rencontres de Moriond, Les Arcs, France, 22-28 March, 1992

W. Kurcewicz, G. Løvhøiden et al. Search for stable octupole deformation in 223Fr and 229Ra 6th International Conference on Nuclei far from Stability, Bernkastel, Germany, July 19-24,1992.

E. Andersen, G.Løvhøiden and the NA36 Collaboration Strangeness production in relativistic nuclear collisions International Nuclear Physics Conference, Wiesbaden, Germany, July 26 - August 1, 1992.

J.M. Nelson, G. Løvhøiden and the NA36 Collaboration Recent Results from the NA36 Experiment, North-West Europe Nuclear Physics Conference, Edinburgh, Scotland, 31 March - 3 April, 1992.

B. de la Cruz, G. Løvhøiden and the NA36 Collaboration Peripheral S+Pb Interactions at 200 A GeV/c; pt distributions, temperature distributions and cross sections, XXII Int. Symp. on Multiparticle Dynam- ics, Santiago de Compostela, Spain, July 13 - 17, 1992, World Scientific, Singapore, to be printed.

E. Andersen, G. Løvhøiden and the NA36 Collaboration Strangeness production in 200 GeV/c p+Pb reactions XXVIIth Rencontres de Moriond, QCD and HIGH Energy Hadronic Interactions

E. Andersen et al. Strangeness production in nucleus-nucleus collisions and proton-nucleus collisions at 200 GeV/c/A 7th Nordic Meeting on Nuclear Physics, Book of Abstracts p. 71, Vigsø, Denmark, August 17-21, 1992.

E. Andersen, G. Løvhøiden et al. Low spin S-band members in 160 162Dy International Nuclear Physics Conference, Wiesbaden, Germany, July 26- August 1, 1992.

R.W. Eriksen, E. Sørbrøden, S. Messelt, A. Olsen On-Line Acquisition of Electron Diffraction Data in TEM Micron and Microscopia Acta 23, 159, 1992.

118 E. Osnes Shell-Model Calculations with Realistic Effective Interactions Invited Talk at the International Workshop ou Nuclear Structure Models, Oak Ridge, Tenn., USA, 16 - 25 March 1992.

E. Osnes Status of Microscopic Effective Interaction Calculations Invited Talk at the International Workshop on Microscopic Nuclear Struc- ture Theory, Institute for Nuclear Theory, University of Washington, Seattle, Wash., USA, 14 - 18 September 1992.

E. Osnes Recent Developments in Effective Interactions

Invited talk at the Technical University, Darmstadt, Germany, 16 July 1992.

E. Osnes Recent Developments in the Calculation of Realistic Effective Interactions Invited talk at the Nuclear Physics Research Center, Jiilich, Germany, 4 August 1992. M. Piiparinen, P. Kleinheinz, J. Blomqvist, A. Vir tanen, . At a?, D. Miiller, J. Nyberg, T. Ramsøy and G. Sletten Two- to One-Phonon E3 Transition Strength in l48Gd Contribution to Int. Conf. on Nuclear Structure at High Angular Momen- tum, Ottawa, May 18-23 1992.

N.L. Gjørup, T. Ramsøy, R. Bark, M. Piiparinen, G. Sletten, P.M. Waker, B.D.D. Singleton, K.C. Yeung, S. M^arai and E. Ideguchi Spectroscopy in the heavy W and Hf nuclei with charged particle channel selection Contribution to Int. Conf. on Nuclear Structure at High Angular Momen- tum, Ottawa, May 18-23 1992.

W. Korten, M.J. Piiparinen, A. Atag, R.A. Bark, B. Herskind, T. Ramsøy, G. Sletten, J. Gerl, H. Hiibel, P. Willsau, B. Cederwall, L.O. Norlin and B. Fant New Results on the Superdeformed Band in 194Pb Contribution to Int. Conf. on Nuclear Structure at High Angular Momen- tum, Ottawa, may 18-23 1992.

J. Rekstad Focus on the Statistical Gamma Decay Inv. talk, The 7th Nordic Meeting on Nuclear Physics, Vigsø, Denmark, 17-21 Aug. 1992.

119 A. Nordlund, A. Ata<;, M. Bergstrom, H. Carlsson, P. Ekstrom, G.B. Hage- mann, B. Herskind, H.J. Jensen, J. Jongman, S. Leoni, A. Maj, J. Nyberg, P.O. Tjørn and H. Ryde The rotational Structure of 1G4Yb 7th Nordic Meeting on Nuclear Physics, Book of abstracts p. 47, Vigsø Kursuscenter, Denmark 17.-21. August 1992.

J.C. Bacelar, M. Bergstrøm, A. Brockstedt, M. Diebel, L. Carlén, L.P. Ek- strøm, S. Frauendorf, J.D. Garrett, G.B. Hagemann, B. Herskind, J. Kow- nacki, J. Lyttkens-Lindén, F. May, H. Ryde, P.O. Tjøm, C.X. Yang High-K States and El-Strength in lc3Er 7th Nordic Meeting on Nuclear Physics, Book of abstracts p. 89 Vigsø Kur- suscenter, Denmark 17.-21. August 1992.

A. Brockstedt, J. Lyttkens-Lindén, M. Bergstrom, L.P. Ekstrom, H. Ryde, J.C. Bacelar, S. Frauendorf, J.D. Garrett, G.B. Hagemann, B. Herskind, F.R. May, P.O. Tjøm Interpretation of bands in 1G3Er within the tilted Rotation Scheme Invite d lecture at the 21st INS International Symposium on Rapidly Ro- tating Nuclei, Tokyo Oct. 26-30 1992.

H.J Whitlow, V. Avdeichikov, M. Guttormsen, B. Jakobsson, J. Nyberg, K. Nybø, A. Oskarsson, L. Westerberg and the CHIC Collabo- ration Development of CHICSI: A multidetector particle telescope for intermediate energy ion physics at CELSIUS 7th Nordic Meeting on Nuclear Physics, Book of abstracts p. 67, Vigsø Kui- suscenter, Denmark 17.-21. August 1992.

K. Gjøtterud Sakharov Memorial Lectures in Physics, Proceedings of the First Interna- tional Sakharov Conference on Physics, Nova Science Publishers, 1992.

11.4.2 Energy Physics

F. Ingebretsen Computer Simulation of the SOLNOR Solar Heating System Proceeding from NORTH SUN '92, Solar Energy at High Lattitudes, June 24-26 (1992) 351-355

F. Ingebretsen Termiske solfangeranlegg, hva slags uata trenger vi? "Sol i Skolen" (SOLIS) seminar, Dalon, Telemark 23-25 sept. 1992.

J. Rekstad Framtidens nøkkelproblem; energiressurser? Noen kommentarer Foredrag ved Det Kongelige Norske Videnskabers Selskap, Trondheim, 7 november 1992.

120 J. Rekstad Termiske energikilder - solenergi Foredrag og artikkel til den 1. nordiske nyskapnings- og arbeidslivsmesse Oslo Plaza, 18 nov. 1992.

T. Bergene Seminar i energifysikk Fysisk Institutt, Universitetet i Oslo des. 1992.

11.4.3 Radiation

T. Strand The Radon Situation in Norway - Sources, Surveys and Mitigation Work Paper presented at the 4th Nordic Conf. on Environmental Health, Kolbing, Denmark, April 7-8, 1992.

11.4.4 Educational Physics

A. Isnes Metode og resultater i SISS-undersøkelsen Forskningsseminar ved pedagogisk Forskningsinstitutt, UiO. 1992.

11.5 Popular Science

K. Gjøtterud "Fysikk og filosofi."

Forelesning Aker Eldreuniversitet Oslo 24.11 1992.

K. Gjøtterud "Romtidsforestillinger i fysikk og matematikk uten formler." Institutt for romkunst Statens kunstakademi 01.12 1992. K- Gjøtterud "Er det forskjell med hensyn til vitenskapelig rasjonalitet i klassisk og kvan- tisk fysikk."

Forelesning Faglig-pedagogisk dag Fysisk institutt UiO 10.01 1992

K. Gjøtterud Har Plancks konstant konsekvenser for naturfilosofien Foredrag Fysikkforeningen UiO 17.11 1992. T. Holtebekk UiO - Epoker i Fysisk Institutts historie Ra Fysikkens Verden 1, 54 1992. 4

121 T. Holtebekk Naturvitenskapsmenn og Teologer i Samtale Kronikk i Vårt Land 20 juli 1992.

T. Holtebekk A.K. Raychaudhuri: Classical Theory of Electricity and Magnetism. Oxford University Press 1990

Bokanmeldelse i Era Fysikkens Verden, vol.54 no. 1 1992. 24.

T. Holtebekk Elgarøy og Hauge: Fra strålende objekter til sorte hull. Del 2. Stjernehim- melen

Bokanmeldelse i Fra Fysikkens Verden no. 1, 54 1992. 23.

G. Løvhøiden FelleskollokviumPå jakt etter kvar, kFysis gluok ninstitutt plasma , UiO, 19 november, 1992.

G. Løvhøiden På jakt etter urstoffet Intervju i "Verdt å vite", NRK, Pl, 26 des. 1992.

S. Messelt, T. Engeland and M. Guttormsen (editors) Section for Nuclear Physics and Energy Physics Annual Report 1991

University of Oslo Report, UiO PHYS 92-09, 1992.

J. Rekstad Solenergi billigst og best ? Intervju i Energi og Miljø 1992. J. Rekstad Solenergi - billigst? Intervju i Impuls nr. 9 1992.

J. R.-kst ad Solnor tar vare på solvarmen Intervju i Tønsbergs Blad 8 juli 1992.

J. Rekstad Intervju (II) i programposten "30 grønne", NRK-P2, 30 nov. 19r2.

J. Rekstad Nytt norsk-ut viklet energitak lanseres Intervju i Varden 2 juli 1992. J. Rekstad Intervju i programposten "Tilfellet Tellus" NRK-TV, 11 og 12 jan. 1992.

122 J. Rekstad Norsk solkollektor med internasjonale ambisjoner Intervju i Arkitektnytt nr. 16, 1992.

J. Rekstad Norsk tak gir huset solvarme Intervju i Aftenposten 8 juli 1992.

J. Rekstad Intervju (I) i programposten "30 grønne", NRK-P2, 27. nov. 1992.

C. Angell, J. Haugan, A. Isnes Fysikk i naturfaget. Fjernundervisning. Modul 3. Vårt fysiske verdensbilde NKI forlaget 1992. C. Angell, J. Haugan, A. Isnes Fysikk i naturfaget. Fjernundervisning. Modul 2. Vår elektriske hverdag NKI forlaget 1992.

C. Angell, J. Haugan, A. Isnes Fysikk i naturfaget. Fjernundervisning. Modul 1. Energi og bevegelse NKI forlaget 1992.

C. Angell, A. Isnes Læringsmiljøet ved Fysisk institutt, UiO Fra Fysikkens Verden Nr 2, 54, 1992, 48

K. Gjøtterud "Uskarphetsrelasjonene - muligheter eller bare problemer?.1' Forelesning Etterutdanningskurs for fysikklærere, Fysisk institutt UiO 01.12.92.

A. Isnes, O.T. Nilsen, A. Sandås Fysikk for teknisk fagskole. Grunnbok, NKI forlaget 1992.

A. Isnes, T. Kristensen, K. Svelle, B. Tysdahl Lærerveiledning til verket Naturfag 7-9, Cappelen 1992.

A. Isnes, O.T. Nilsen, A. Sandås Fysikk for teknisk fagskole. Arbeidsbok med laboratorieøvinger NKI forlaget 1992.

A. Isnes, O.T. Nilsen, A. Sandås Fysikk for teknisk fagskole. Fasit med løsningsforslag NKI forlaget \992.

A. Isnes Naturfagundervisning på ungdomstrinnet Lærerkurs, Cappelen Forlag A/S 10 mars 1992.

123 A. Is nes Praktisk naturfag på ungdomstrinnet Lærerkurs, Skolesjefen i Oslo, 20 mars 1992.

A. Isnes Undervisning om lyd og støy Lærerkurs, Skolesjefen i Stavanger 19 nov. 1992.

T. Bergene Fysikere og filosofer Kronikk i Dagbladet 9 1992.

11.6 Science Policy

0. Holter og F. Ingebretsen Fra Redaktørene

Fra Fysikkens Verden, Vol. 54 no. 1,2,3,4 1992.

LærerutdanningeA. Isnes n som profesjonsutdanning - hva nå? Konferanse om lærerutdanning. Lærerutdanningsrådet, Oslo 9 nov. 1992.

A. Isnes Synspunkter på dagens og morgendagens realfagsundervisning i skolen Jubileumskonferanse, Skolelaboratoriet, Univ. i Bergen 16 nov. 1992.

E. Osnes og J. Rekstad Norsk kjernefysikks grunnlegger professor Roald Tangen 80 år Aftenposten 7. februar 1992.

124 FYSISK INSTITUTT DEPARTMENT OF FORSKNINGS- PHYSICS GRUPPER RESEARCH SECTIONS

Biofysikk Biophysics Elektronikk Electronics Elementærpartikkelfysikk Experimental Elementary Particle physics Faste staffers fysikk Condensed Matter physics Kjernefysikk Nuclear physics Plasma-, molekylar- og Plasma-, Molecular and kosmisk fysikk Cosmic physics Strukturfysikk Structural physics Teoretisk fysikk Theoretical physics

ISSN • 0332 - 5371